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Posted: Mar 10, 2010

Nanotoxicology - mammalian and plant cells respond differently to fullerenes

(Nanowerk Spotlight) Some scientists believe that, with the increased mass production of engineered nanoparticles like carbon nanotubes, there is a realistic chance for these particles to interact with water, soil and air, and subsequently enter the food chain (see: "Starting to explore nanotechnology's impact on major food crops"). However, understanding the behavior and impacts of nanomaterials in the environment and in human health is a daunting task. The cynics argue that it is impossible to fully explore the toxicological impact of every existing and future nanomaterial with its many millions of variants, so why bother with a few half-hearted and underfunded research projects. Rather, let's wait until nanotechnology has its asbestos moment and some people drop dead – then we have something concrete to look into.
People who are taking a more thoughtful approach to the complexities of nanotoxicological research agree that most likely we never will have full scientific certainty about the environmental and health impact of nanomaterials. Today we don't even know what the impact of most chemicals is, and that includes products we have been using for many years. Nevertheless, a general understanding about nanotoxicity is slowly emerging as the body of research on cytotoxicity, genotoxicity, and ecotoxicity of nanomaterials grows. In our Spotlight today we take a look at new biophysical research – a parallel study of carbon-nanoparticle uptake by plant and mammalian cells – that contributes to the general picture of the fundamental behaviors of nanoparticles in both biological and ecological systems.
"While biological and ecological systems constantly interact and are integrated in the network of nature, it remains a new challenge to evaluate and correlate the biological and environmental impacts of nanoparticles within the same context," Pu-Chun Ke tells Nanowerk. "Our study provides a first parallel comparison on the uptake of carbon nanoparticles by plant Allium cepa and mammalian HT-29 cells. We have identified these two key factors in determining the fate of nanoparticles in biological and ecological systems: the structure of the host cell, and the physiochemistry of the nanoparticles. These two factors are integrated in any systems involving both synthetic nanoparticles and living organisms."
TEM imaging of carbon nanoparticle uptake by Allium cepa plant cell
TEM imaging of carbon nanoparticle uptake by Allium cepa plant cell. (Images: Dr. Ke, Clemson University)
In previous work ("The Differential Cytotoxicity of Water-Soluble Fullerenes"), it was discovered that pristine nanoparticles could induce damage in mammalian cells while well-functionalized fullerene nanoparticles are far more biocompatible. Ke, an associate professor at Clemson University, who leads the Single-Molecule Biophysics and Polymer Physics Laboratory, explains that this differential toxicity stems from the hydrophobic interior of the lipid bilayer which promotes the partitioning of the hydrophobic nanoparticles.
"In other words the energy penalty would be quite high for well-solubilized nanoparticles to be taken up by a mammalian cell, unless the biological process of endocytosis overwrites the physical process of passive diffusion and thermodynamics. Our study suggests that the supramolecular assembly of C70 suspended in natural organic matter (C70-NOM), due to its non ideal solubility, behaved similarly to pristine C70 nanoparticles in mammalian cells."
Ke and his team found that in the presence of a (hydrophobic, rigid) plant cell wall, well-solubilized fullerene derivative C60(OH)20 nanoparticles readily translocated across the cell wall and accumulated at the interface between the cell wall and the (fluidic and amphiphilic) plasma cell membrane. At high nanoparticle concentrations such accumulation would mechanically protrude through the cell membrane to induce cell damage. By comparison, less-solubilized fullerene C70-natural organic matter complexes were mostly trapped in the porous plant cell wall, and therefore imposed little effect on plant cell viability.
"For mammalian cells we have found that C60(OH)20 nanoparticles were largely bio-benign, while C70-NOM caused increased cell damage with its increased concentration" says Ke. "This research tells us that even for the same nanoparticles they may exert contrasting effects on biological and plant hosts due to the presence of an extra plant cell wall in the latter. For the same host systems, mammalian or plant cells included, nanoparticles may as well induce contrasting cell damage due to their different hydrophilicity."
The results from this work could be exploited in two ways: mitigating the toxicity of nanoparticles for their biosensing and imaging applications; and designing drug and gene delivery strategies to mammalian and plant systems with a nanoparticle transporter of appropriately designed surface properties.
Research like this is inherently multidisciplinary in its nature, requiring scientists with different backgrounds, both in experimental and simulation fields, to collaborate. In this particular case, the research is characterized by its distinct biophysical nature.
"The basic components of our research are supramolecular assembly, molecular cell biology, and thermodynamics" explains Ke. "We believe such fundamental research is needed for describing the complex behaviors of nanoparticles in biological and ecological systems, which serve as the basis for understanding the biological and environmental implications and applications of nanomaterials."
The researchers have published their findings in the March 8, 2010 online issue of Small ("Differential Uptake of Carbon Nanoparticles by Plant and Mammalian Cells").
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