Exposure to carbon nanotube material: assessment of nanotube cytotoxicity using human keratinocyte cells.
Exposure to carbon nanotube material:
assessment of nanotube cytotoxicity using human keratinocyte cells.
Shvedova AA, Castranova V
Summary:
In this paper, the authors studied the adverse affects of single-walled carbon nanotubes (SWCNT) that are exposed to human epidermal keratinocytes. They performed these tests because carbon nanotubes, a relatively new particle, have been shown to have novel properties that have potential use in the medical world. These applications include drug delivery, cancer treatment, and a device strengthening. The paper was mostly interested in the oxidative stressed that was placed on the cells and the morphological changes that took place in the cell.
To measure the oxidative stress placed on the cells, there were many approaches taken. The first was to detect the free radicals present in the cell. They used ESR spin trapping to detect free radicals by recording the spectrum from the mixture containing the cells exposed to the SWCNTs. The results indicated a large free radical OH production that was SWCNT stimulated.
In order to determine if this stress caused a morphological change in the cells, scanning and transmission microscopy of the cells was used. Transmission microscopy showed that there were cell morphological changes in the nucleus, mitochondria, tonofiliments, and other cytoplasmic organelles.
Conclusions:
The paper concluded that it is the catalytic iron that is used in the production of nanotubes that causes the oxidative stress that is present in the cells. This comes from nanotubes that are not refined. Unrefined nanotubes have been shown to contain 30% iron composition. The iron has the ability to catalyze one electron reactions leads to the extra oxidative stressed placed on the cells.
Relevance:
This paper is relevant to my project because of the many biological uses that nanotubes may have in the future. We are interested in the effects of nanotubes on cells because of the therapeutic potential that they hold in the medical world. After reading the conclusion, it is slightly off topic from the reasons I am pursuing the question about the effects of nanotubes on cells. Since they concluded that iron places this stress on the cells, simply refining the nanotubes can fix the problem. We are more interested in the actual carbon structure, and the effects it makes on the cells. It is still important to realize that the refinement of nanotubes is important in biocompatibility, and it is important to know that if we use unrefined nanotubes in our experiment, it can alter our results.
7 comments:
Have there been similar studies run on refined SWCNTs to confirm the conclusions proposed by this paper? In many studies, experiments push environments to the extreme. Were the SWCNTs allowed to oxidize naturally, or were the cells manipulated in order to induce iron oxidation? How severe was the oxidative damage? Did it lead to any cell death, or loss of function? Do you feel it would be dangerous to use the unrefined SWCNTs in medicinal therapies?
What are the specific benefits to using carbon nanotubes for drug delivery? If it is dangerous for the nanotubes to oxidize/breakdown in vivo, then it seems like sustained carbon nanotube therapy would result in a build-up of carbon inside cells. Is there a way for cells to safely metabolize these nanotubes, or to otherwise rid them from the body?
Did the paper mention any specifics ways in which the carbon nanotubes could be modified or refined so that they would not induce such a strong oxidative reaction? Might there be a way to potentially mark them for breakdown (once their purpose is fulfilled) by some sort of cellular/body mechanism?
Did the authors of the paper mention how realistic it is to make materials composed completely of refined nanotubes? Essentially, I'm wondering if process limitations exist such that it's impossible to expect every nanotube to be refined. In this case, it'd also be good to know how detrimental the oxidative stress is to cells. Do the authors mention anything about an acceptable range of recoverable stress that the cells can experience?
Maybe an animal model would be best in assessing CNT toxicity. I've read that CNTs tend to accumulate in certain tissues or organs, like the liver. In such an experiment, the researcher has to be very careful to eliminate all confounding variables to determine that CNTs cause oxygen radical buildup which leads to cell damage. Were the controls properly set up to make this conclusion? Without further experiments, especially in an animal model, I don't feel like I can generalize this paper's conclusion to general CNT toxicity. What do you think?
If there is no easy method of making the SWCNTs less oxidative, could you include additional components (like antioxidants) that would mitigate the stress placed on the cells? I am assuming that free radicals created by the nanotubes is what causes the oxidative stress. If nanotubes are used in device strengthening, is there a way to cover the nanotubes themselves so that the negative effect on the cells is reduced?
Responses:
Jennifer:From what the paper states, it was natural oxidation that was taking place with the SWCNTs. The only thing done to the cells was that there were exposed to the nanotubes. This exposure was leading to cell death eventually, which is the entire reason this study was published.
Carbon nanotubes themselves are very useful, it is the iron that is used in production that is cytotoxic. This biggest issues is the metabolism/getting rid of the tubes issue. Current studies say that the tubes are safe, but it is not known if long term treatments will cause an accumulation.
Dana: The paper only mentioned that finding another catalyst to take the place of the iron would reduce the amount oxidation that takes place. Because there are only crude methods known for breaking down the nanotubes which would not be possible for the body.
Eric: Thought the authors did not mention it, other readings have told me that it is very hard to control and refine nanotubes. There are new techniques being developed, but they often involve chemical processes that are detrimental to biological application.
The authors did not mention a threshold for oxidative stress and would be important to understand once clinical application begins.
Lavanya: The controls were properly set up, though this was a study on cells in vitro. They did not delve into issues with buildup in tissues, which is another important next step in research.
I don't think the paper was getting at the fact that CNTs were in general toxic, yet I think that they were saying that CNTs produced with Fe catalyst have residual iron which is cytotoxic.
Chris: I think all of your points are very innovative. If antioxidants were to be implemented, they would to need not interfere with the SWCNT refinement process. Since CNTs are built atom by atom, this could cause a problem.
I definitely believe there would be a novel way to cover the CNTs with a bio-compatible material to prevent the oxidation. If it were just for strengthening, then it is just necessary to make sure that the cells are not in contact or are not interacting with the CNTs.
You mention that carbon nanotubes have novel properties with many clinical applications (drug delivery, cancer treatment, and a device strengthening). Could you elaborate on what exactly a nanotube does and what these novel properties are? Does it have to do with the structure of the nanotube, interactions, etc? Also, what exactly does oxidative stress do to a nanotube?
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