We have shown previously that single-walled carbon nanotubes can be catalytically biodegraded over several weeks by the plant-derived enzyme, horseradish peroxidase. However, whether peroxidase intermediates generated inside human cells or biofluids are involved in the biodegradation of carbon nanotubes has not been explored. Here, we show that hypochlorite and reactive radical intermediates of the human neutrophil enzyme myeloperoxidase catalyse the biodegradation of single-walled carbon nanotubes in vitro, in neutrophils and to a lesser degree in macrophages. Molecular modelling suggests that interactions of basic amino acids of the enzyme with the carboxyls on the carbon nanotubes position the nanotubes near the catalytic site. Importantly, the biodegraded nanotubes do not generate an inflammatory response when aspirated into the lungs of mice. Our findings suggest that the extent to which carbon nanotubes are biodegraded may be a major determinant of the scale and severity of the associated inflammatory responses in exposed individuals.

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.

H uman noroviruses are the leading cause of outbreaks of acute gastroenteritis, associated with ≈50% of all outbreaks worldwide (1). Norovirus outbreaks are frequently reported in semiclosed institutions, such as hospitals, nursing homes, schools, and childcare centers (2). The virus is primarily transmitted directly from person to person or indirectly through contaminated surfaces, food, or water (1). The relative stability of noroviruses on environmental surfaces makes infection control challenging (3). Several candidate norovirus vaccines are in clinical trials (4). Noroviruses are single-stranded RNA viruses that belong to the genus Norovirus, family Caliciviridae. The genome is organized into 3 open reading frames (ORFs): ORF1 encodes polyprotein, ORF2 encodes the major capsid protein (VP1), and ORF3 encodes the minor (VP2) capsid protein. The viruses are classified into at least 7 genogroups (G), of which viruses from GI, GII, and GIV infect humans (5,6). On the basis of the diversity of VP1, these genogroups can be further divided into at least 33 genotypes: 9 GI, 22 GII, and 2 GIV (7). In addition, on the basis of the diversity of the polymerase region of ORF1, >14 GI polymerase (GI.P) types and 27 GII.P types have been described (7). Because of the frequent recombination at the ORF1/ORF2 junction region, a dual-typing system has been proposed for GI and GII noroviruses (7). Since 2002, genogroup II, genotype 4 (GII.4), noroviruses have been associated with most norovirus outbreaks globally, and new GII.4 variants have emerged every 2-3 years (8). Monitoring the trends in the distribution of the various genotypes and possible association of certain strains with a more severe disease outcome is important for understanding and controlling norovirus epidemics (9). Several norovirus outbreak surveillance networks, including NoroNet (10) and CaliciNet (7,11), have been developed during the past decade. NoroNet captures molecular and epidemiologic data on norovirus outbreaks and sporadic cases submitted by 19 participating countries across Europe and Asia and by Australia. CaliciNet is a norovirus outbreak surveillance network in the United States in which state and local public health laboratories electronically submit laboratory data, including sequences from norovirus outbreaks, to a central database (https://www. cdc.gov/norovirus/reporting/calicinet/data.html). CaliciNet data are integrated with epidemiologic data

The risk of radionuclide release in terrorist acts or exposure of healthy tissue during radiotherapy demand potent radioprotectants/radiomitigators. Ionizing radiation induces cell death by initiating the selective peroxidation of cardiolipin in mitochondria by the peroxidase activity of its complex with cytochrome c leading to release of hemoprotein into the cytosol and commitment to the apoptotic program. Here we design and synthesize mitochondria-targeted triphenylphosphonium-conjugated imidazole-substituted oleic and stearic acids which blocked peroxidase activity of cytochrome c/cardiolipin complex by specifically binding to its heme-iron. We show that both compounds inhibit pro-apoptotic oxidative events, suppress cyt c release, prevent cell death, and protect mice against lethal doses of irradiation. Significant radioprotective/radiomitigative effects of imidazole-substituted oleic acid are observed after pretreatment of mice from 1 hr before through 24 hrs after the irradiation.

Broad applications of single-walled carbon nanotubes (SWCNT) dictate the necessity to better understand their health effects. Poor recognition of non-functionalized SWCNT by phagocytes is prohibitive towards controlling their biological action. We report that SWCNT coating with a phospholipid “eat-me” signal, phosphatidylserine (PS), makes them recognizable in vitro by different phagocytic cells - murine RAW264.7 macrophages, primary monocyte-derived human macrophages, dendritic cells, and rat brain microglia. Macrophage uptake of PS-coated nanotubes was suppressed by the PS-binding protein, Annexin V, and endocytosis inhibitors, and changed the pattern of pro- and anti-inflammatory cytokine secretion. Loading of PS-coated SWCNT with pro-apoptotic cargo (cytochrome c) allowed for the targeted killing of RAW264.7 macrophages. In vivo aspiration of PS-coated SWCNT stimulated their uptake by lung alveolar macrophages in mice. Thus, PS-coating can be utilized for targeted delivery of SWCNT with specified cargoes into professional phagocytes, hence for therapeutic regulation of specific populations of immune-competent cells.