4 research outputs found
Dual Enzyme-like Activities of Iron Oxide Nanoparticles and Their Implication for Diminishing Cytotoxicity
Iron oxide nanoparticles (IONPs) are frequently used in biomedical applications, yet their toxic potential is still a major concern. While most studies of biosafety focus on cellular responses after exposure to nanomaterials, little is reported to analyze reactions on the surface of nanoparticles as a source of cytotoxicity. Here we report that different intracellular microenvironment in which IONPs are located leads to contradictive outcomes in their abilities to produce free radicals. We first verified pH-dependent peroxidase-like and catalase-like activities of IONPs and investigated how they interact with hydrogen peroxide (H<sub>2</sub>O<sub>2</sub>) within cells. Results showed that IONPs had a concentration-dependent cytotoxicity on human glioma U251 cells, and they could enhance H<sub>2</sub>O<sub>2</sub>-induced cell damage dramatically. By conducting electron spin resonance spectroscopy experiments, we showed that both Fe<sub>3</sub>O<sub>4</sub> and γ-Fe<sub>2</sub>O<sub>3</sub> nanoparticles could catalyze H<sub>2</sub>O<sub>2</sub> to produce hydroxyl radicals in acidic lysosome mimic conditions, with relative potency Fe<sub>3</sub>O<sub>4</sub> > γ-Fe<sub>2</sub>O<sub>3</sub>, which was consistent with their peroxidase-like activities. However, no hydroxyl radicals were observed in neutral cytosol mimic conditions with both nanoparticles. Instead, they decomposed H<sub>2</sub>O<sub>2</sub> into H<sub>2</sub>O and O<sub>2</sub> directly in this condition through catalase-like activities. Transmission electron micrographs revealed that IONPs located in lysosomes in cells, the acidic environment of which may contribute to hydroxyl radical production. This is the first study regarding cytotoxicity based on their enzyme-like activities. Since H<sub>2</sub>O<sub>2</sub> is continuously produced in cells, our data indicate that lysosome-escaped strategy for IONP delivery would be an efficient way to diminish long-term toxic potential
Prussian Blue Nanoparticles as Multienzyme Mimetics and Reactive Oxygen Species Scavengers
The
generation of reactive oxygen species (ROS) is an important
mechanism of nanomaterial toxicity. We found that Prussian blue nanoparticles
(PBNPs) can effectively scavenge ROS via multienzyme-like activity
including peroxidase (POD), catalase (CAT), and superoxide dismutase
(SOD) activity. Instead of producing hydroxyl radicals (•OH)
through the Fenton reaction, PBNPs were shown to be POD mimetics that
can inhibit •OH generation. We theorized for the first time
that the multienzyme-like activities of PBNPs were likely caused by
the abundant redox potentials of their different forms, making them
efficient electron transporters. To study the ROS scavenging ability
of PBNPs, a series of in vitro ROS-generating models was established
using chemicals, UV irradiation, oxidized low-density lipoprotein,
high glucose contents, and oxygen glucose deprivation and reperfusion.
To demonstrate the ROS scavenging ability of PBNPs, an in vivo inflammation
model was established using lipoproteins in Institute for Cancer Research
(ICR) mice. The results indicated that PBNPs hold great potential
for inhibiting or relieving injury induced by ROS in these pathological
processes
Sources and Processes Affecting Fine Particulate Matter Pollution over North China: An Adjoint Analysis of the Beijing APEC Period
The
stringent emission controls during the APEC 2014 (the Asia-Pacific
Economic Cooperation Summit; November 5–11, 2014) offer a unique
opportunity to quantify factors affecting fine particulate matter
(PM<sub>2.5</sub>) pollution over North China. Here we apply a four-dimensional
variational data assimilation system using the adjoint model of GEOS-Chem
to address this issue. Hourly surface measurements of PM<sub>2.5</sub> and SO<sub>2</sub> for October 15-November 14, 2014 are assimilated
into the model to optimize daily aerosol primary and precursor emissions
over North China. Measured PM<sub>2.5</sub> concentrations in Beijing
average 50.3 μg m<sup>–3</sup> during APEC, 43% lower
than the mean concentration (88.2 μg m<sup>–3</sup>)
for the whole period including APEC. Model results attribute about
half of the reduction to meteorology due to active cold surge occurrences
during APEC. Assimilation of surface measurements largely reduces
the model biases and estimates 6%–30% lower aerosol emissions
in the Beijing–Tianjin–Hebei region during APEC than
in late October. We further demonstrate that high PM<sub>2.5</sub> events in Beijing during this period can be occasionally contributed
by natural mineral dust, but more events show large sensitivities
to inorganic aerosol sources, particularly emissions of ammonia (NH<sub>3</sub>) and nitrogen oxides (NO<sub><i>x</i></sub>) reflecting
strong formation of aerosol nitrate in the fall season