查看完整版本: Nanoparticle penetration of human skin – a double-edged sword

Nanoparticle penetration of human skin – a double-edged sword

Engineered nanoparticles are at the forefront of the rapidly developing field of nanomedicine. Their unique size-dependent properties, of which optical and magnetic effects are the most used for biological applications, makes them suitable for a wide range of biomedical applications such as cell labeling and targeting, tissue engineering, drug delivery and drug targeting, magnetic resonance imaging, probing of DNA structure, tumor destruction via heating (hyperthermia), and detection and analysis of biomolecules such as proteins or pathogens. Many of these applications can also be tailored to target skin to help in the early diagnosis of a skin disease, which then could also be treated via nanocarriers. In addition, a tissue engineering approach could be useful for skin wound healing therapies and the magnetic properties of these particles might help in directing and localizing these agents in a particular layer of the skin where their action is desired. Unfortunately, if nanoparticles are able to penetrate layers of skin for therapeutic purposes, they might equally be able to penetrate skin unintentionally. [color=Red]This raises the question if people, who are exposed to such nanomaterials, could accidentally be contaminated and thus exposed to a potential local and/or systemic health risk[/color]. Researchers in Italy now have begun to systematically evaluate both risks and applications of nanoparticle skin absorption.

The discussion about the safety of engineered nanoparticles has become quite polarized, with one side – activist groups – emphasizing the potential risks (e.g. "[b]Nanomaterials, sunscreens and cosmetics: Small ingredients, big risks[/b]" - pdf download 1.42 MB) and the other – the cosmetics industry – claiming that there is no reason for concern "[b]Nanoparticles and the skin - a health risk for the consumer?[/b]" - pdf download 2.7 MB).
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The existing literature on the ability of nanoparticulate material to penetrate skin is inconclusive at best. We reported on one recent research finding in a previous Nanowerk Spotlight that showed that fullerene-based peptides can penetrate intact skin and that mechanical stressors, such as those associated with a repetitive flexing motion, increase the rate at which these particles traverse into the dermis ("Fullerenes shown to penetrate healthy skin").

Researchers in Italy have investigated whether superficially modified iron-based nanoparticles, not designed for skin absorption but whose dimensions are compatible with those of skin penetration routes, are able to penetrate and perhaps permeate the skin. Their results, which showed profound skin penetration by these nanoparticles, opens up two main directions of investigation: a) nanomaterial toxicological risk assessment and awareness, b) potential exploitation of nanomaterials as carriers for drug delivery into and through the skin.

"So far, the skin, which is our first defense against the environment, has been considered an unlikely path of entry for engineered nanoparticles" Dr. Biancamaria Baroli explains to Nanowerk. "Yet these conclusions arise from investigations carried out with much bigger particulate vehicles than the ones we used (< 10 nm). Even bacteria and viruses are bigger; for instance, the dimension of adenovirus is around 150 nm. We think that the question, whether such small materials could penetrate and permeate the skin, is an important question to be asked."

Baroli, a researcher at the Department of Pharmacy at the University of Cagliari, is first author of a recent paper in Journal of Investigative Dermatology titled "[url=http://www.nature.com/jid/journal/vaop/ncurrent/abs/5700733a.html][b]Penetration of Metallic Nanoparticles in Human Full-Thickness Skin[/b][/url]".
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[URL=http://www.nanost.net/bbs/thread-7363-1-1.html][IMG]http://img409.imageshack.us/img409/1382/id182012b47a9zx9.jpg[/IMG][/URL]
[i]TMAOH ((tetramethylammonium hydroxide)-maghemite nanoparticle characterization and recovery within human skin after few hours of contact. Nanoparticles appeared to passively penetrate the skin through the transepidermal and transfollicular routes. A) Macroscopic appearance of a TMAOH-maghemite nanoparticle aqueous dispersion. B) TEM micrograph of TMAOH-maghemite nanoparticles. C) Hematoxylin-stained human skin exposed to TMAOH-maghemite nanoparticles. Using a light transmission microscope, nanoparticles are visible in the stratum corneum (yellow line) as brown areas. Unfortunately, digitalization does not allow to see smaller deposits in viable epidermis (pink line) or dermis (blue line). D) EDS-SEM micrograph showing nanoparticle deposits (white spots) within the stratum corneum, stratum corneum-viable epidermis junction, and a little below the junction. E) EDS spectrum of white spots within D, showing the presence of iron. (Images: Dr. Baroli)[/i]

In their recent work, Baroli and her collaborators applied two different stabilized nanoparticle dispersions to human skin samples. The results of this study showed that nanoparticles were able to passively penetrate the skin and reach the deepest layers of the stratum corneum (SC – the outermost layer of the skin) and hair follicle and, occasionally, reach the viable epidermis. Yet, nanoparticles were unable to permeate the skin. From a therapeutic point of view, these results represent a breakthrough in skin penetration because it is early evidence where rigid nanoparticles have been shown to passively reach the viable epidermis through the SC lipidic matrix.

"Our findings are in agreement with previously published results" says Baroli. "Although more experiments are needed to help us completely understand the penetration mechanism, this study represents a proof of principle and provides a major breakthrough in the study of skin absorption, which allows us to envisage potential toxicological risks and further nanoparticle biomedical applications.

"In fact, it is now possible to foresee synthesized particles that have been designed specifically to target the skin (as we are currently doing), both to understand the penetration mechanism and to study whether penetrated amounts could be of any use in biomedical applications. In addition, from a nanotoxicological point of view, one can question 'how much is enough' to trigger toxicological responses."

Unfortunately, researchers cannot answer this last question yet, as nanotoxicological risk assessment investigations have only recently been undertaken and the cutaneous route of exposure has not yet received great attention. Baroli points out that her team's commitment is instead to evaluate both risks and applications of nanoparticle skin absorption, hoping that their work will help to increase awareness and safety of a technology with great therapeutic potential.

"We are now investigating nanoparticles designed and synthesized for skin applications with the intent of better understanding penetration mechanisms and to finding simple but accurate methods for quantifying the amount of particles entered into the skin" says Baroli. "A better understanding of penetration mechanisms and our ability of finding methods to quantify particles in the skin may help to develop new nanoparticle-based formulations but also prevent accidental contamination and health risks."

By Michael Berger, Copyright 2007 Nanowerk LLC

[quote]
[table][tr][td][size=4][b]Fullerenes shown to penetrate healthy skin    [/b][/size]                                    [/td][/tr]                                        [tr][td]Nanoparticles exhibit unique properties that make them ideal for awide-variety of applications. Also unique, and largely unknown, are theinteractions that occur between the biological environment andnanoparticles. On the upside, the ability of quantum dots andfullerenes to penetrate intact skin provides potential benefits for thedevelopment of nanomaterial applications involving drug delivery. Onthe downside, this ability poses potential risks associated withmanufacturing and handling such nanoparticles. A new study now confirmsthat fullerene-based peptides can penetrate intact skin and thatmechanical stressors, such as those associated with a repetitiveflexing motion, increase the rate at which these particles traverseinto the dermis. These results are important for identifying externalfactors that increase the risks associated with nanoparticle exposureduring manufacturing or consumer processes. Future assessments ofnanoparticle safety should recognize and take into account the effectthat repetitive motion and mechanical stressors have on nanoparticleinteractions with the biological environment. Additionally, theseresults could have profound implications for the development ofnanoparticle use in drug delivery, specifically in understandingmechanisms by which nanoparticles penetrate intact skin. [/td][/tr]                                        [tr][td=2,1]"Our work investigates how a specific type of nanoparticle, an aminoacid-derivatized fullerene, interacts with the biological environmentboth at the tissue and cellular levels" Jillian Rouse, a student at the[url=http://cctrp.ncsu.edu/index.html]Center for Chemical Toxicology Research and Pharmacokinetics[/url](CCTRP) at North Carolina State University, explains to Nanowerk. "Itis important to identify those nanoparticles that can penetrate intactskin and to determine the potential risk for toxicity once theparticles are in the body. Nanoparticles have the potential to providegreat scientific developments; however, if there are inherentbiological risks associated with their use, then safety evaluationsneed to be conducted." [/td][/tr]                                        [tr][td]Rouse is first author of a recent paper, titled [url=http://dx.doi.org/doi:10.1021/nl062464m]"Effects of Mechanical Flexion on the Penetration of Fullerene Amino Acid-Derivatized Peptide Nanoparticles through Skin"[/url], that was published in the December 6, 2006 web edition of [i]Nano Letters[/i].This study was funded by the Environmental Protection Agency, theNational Academies Keck Futures Initiative and the Robert A. WelchFoundation. [/td][/tr]                                        [tr][td]Rouse, [url=http://www.cvm.ncsu.edu/docs/nancy_monteiro-riviere.html]Dr. Nancy Monteiro-Riviere[/url], professor of investigative dermatology and toxicology at NC State's College of Veterinary Medicine, and [url=http://python.rice.edu/%7Earb/Barron.html]Dr. Andrew R. Barron[/url],professor of chemistry and materials science at Rice University are thefirst to show the ability of fullerenes to penetrate intact skin and torelate nanoparticle penetration to biomechanical stimuli. [/td][/tr]                                        [tr][td]"Our work was motivated by the discovery that mechanical stimuliapplied during standard physiological processes, such as walking,increase thepenetration of particles found in soil and result in a higherprevalence of [url=http://en.wikipedia.org/wiki/Podoconiosis]podoconiosis[/url]in the African rift valleys" says Rouse. "The ability of normalbiomechanical movements to increase nanoparticle penetration solidifiesthe need for risk assessment, especially in occupational settings whereconstant, repetitive motions are involved." [/td][/tr]                                        [tr][td=2,1]The researchers have previously reported the synthesis of thephenylalanine-based fullerene amino acid, Bucky amino acid (Baa), andthe uptake and interaction of Baa with human epidermal keratinocytes ([url=http://dx.doi.org/doi:10.1016/j.tiv.2006.04.004]"Fullerene-based amino acid nanoparticle interactions with human epidermal keratinocytes"[/url]).The presence of the fullerenesubstituent has a significant effect on the intracellular transport ofpeptides containing Baa. The addition of a fullerene-derived amino acidto a cationic peptide results in the peptide showing cellular uptake,whereas the same peptide sequence in the absence of Baa shows notransport across the cell membrane. [/td][/tr]                                        [tr][td]The peptide sequence used is based on on the nuclear localizationsequence (NLS). After the NLS sequence (Pro-Lys-Lys-Lys-Arg-Lys-Val)was completed, a Lys(Mtt) residue was coupled to the end to allowattachment of the fluorescein isothiocyanate (FITC) fluorescent marker.The individual Baa-Lys(FITC)-NLS particles measured ca. 3.5 nm in size.[/td][/tr]                                        [tr][td]Because of its physiological and structural similarities to human skin,porcine skin was used a model for human skin in this study. Todetermine the effects of flexing on skin penetration, the dermatomedskin was dosed with 20 µL of Baa-Lys-(FITC)-NLS in 1% PBS, and thedosed areaswere subsequently flexed for 60 or 90 min or left unflexed (control) toinvestigate nanoparticle penetration. [/td][/tr]                                        [tr][td][img]http://www.nanowerk.com/spotlight/id1210.jpg[/img][/td][/tr]                                        [tr][td=2,1]Confocalscanning microscopy images of skin dosed with Baa-Lys(FITC)-NLS for 24h. Top row: confocal-DIC channel image shows an intact stratum corneum(SC) and underlying epidermal (E) and dermal layers (D). Middle row:Baa-Lys(FITC)-NLS fluorescence channel (green) and confocal-DIC channelshow fullerene penetration through the skin. Bottom row: fluorescenceintensity scan of Baa-Lys(FITC)-NLS. All scale bars represent 50 µm.(Reprinted with permission from the American Chemical Society) [/td][/tr]                                                                                [tr][td]"After 24 h of Baa-Lys(FITC)-NLS treatment, skin penetration wasgreater in all experimental groups" explains Rouse. "The DIC(Differential Interference Contrast) images reveal a thick, intactstratum corneum and the intensity maps show the highest concentrationof particles in the upper epidermal layers and a lower concentration asthe fullerenes penetrate into the dermis. Skin flexed for 90 min showedthe greatest amount of dermal penetration, evident by the higherfluorescence intensity of the nanoparticles in this group (bottom rowin above image)." [/td][/tr]                                        [tr][td]The mechanical loading regimes used in this study attempt to mimicphysiological forces that can occur during nanoparticle manufacturingprocesses or conditions involved in consumer use. The external forcesapplied to the skin while flexing proves to have a significant effecton both the rateand extent of fullerene penetration. Skin flexed for 90 min showsevidence of dermal penetration after 8 h of nanoparticle exposure,whereas control specimens show evidence of fullerenes primarilylocalized in the epidermis and only a slight amount in the dermis afterthe 24 h treatment. [/td][/tr]                                        [tr][td]These results suggest that the action of a flexing procedure increasesthe rate at which fullerenes can penetrate through the skin.Furthermore, flexing increased the amount of fullerenes that werecapable of penetrating into the dermal layers of skin, indicated by thehigher fluorescence intensity of fullerenes for both 60 and 90 minflexed skin. [/td][/tr]                                        [tr][td=2,1]"It is important to note that for all treatments nanoparticlepenetration was non-homogeneous probably due to a nonuniformdistribution of the dose over the dose region and/or differences in thethickness of the epidermis" Rouse points out. [/td][/tr]                                        [tr][td]The route of nanoparticle penetration through the skin is of greatinterest, especially in the nanomedicine field. In this study, TEMdepicted derivatized fullerenes localized within intercellular spacesof the epidermis, suggesting that migration through the skin occursintercellularly as opposed to movement through cells. The findings alsoindicate that fullerene penetration occurs via a mechanism of passivediffusion. Therefore, movement of the derivatized nanoparticles throughthe skin is dependent on the hydrophobic lipid entities that arepresent between the epidermalcells. [/td][/tr]                                        [tr][td]For drug-delivery applications, the ability of nanoparticles to haveaccess to systemic circulation has important implications. However,because some nanoparticles have been shown to initiate adversebiological responses, there are potential risks for systemic toxicityto occur and, therefore, the need arises for risk assessment and theestablishment of safety regulations. [/td][/tr]                                        [tr][td]An important conclusion from this research is that investigations ofthe interactions that occur between nanoparticles and the biologicalenvironment should take into account external stimuli, such asphysiologically relevant biomechanical forces. Whether for nanoparticlerisk assessment or for the development of nano-drug delivery systems,it is important to identify all factors that could influence how theseparticles interact with the body. [/td][/tr]                                        [tr][td=2,1][i]By Michael Berger, Copyright 2007 Nanowerk LLC[/i][/td][/tr][/table]
[/quote]

[[i] 本帖最后由 nanoquebec 于 2007-04-29 19:16 编辑 [/i]]

好文章，支持楼主，五一快乐！！！

回复 #1 nanoquebec 的帖子

看来接触有些纳米粒子要小心。特别是一些改性过的。多用安全手套！

呵呵，这个研究领域有些敏感。纳米粒子的皮肤穿透的争议一直存在。在化妆品行业，纳米粒子的广泛应用及巨大的潜在前景，他们也发表了不少文章支持纳米粒子不能穿透皮肤，或仅能停留于角质层。但一些毒理学家表示怀疑。

记得前不久看过的一篇文献，结论是纳米粒子只能到达角质层，而难于到达皮肤表皮层。令人感到有意思的是，作者在文后甚至附上conflict of interest statement. 以撇清研究者与某些利益集团并没有任何关系，呵呵，恐落人口实。

由此联想到国内某些为利益集团摇旗呐喊的学者们(尤以经济学界为甚)，呵，学术的良心及自由，路还很漫长呀。

呵呵呵，来学习学习。。。

:handshake :victory:

很有兴趣，可惜没条件研究

回复 1# 的帖子

good work, worth to have a look

感谢你的分享啊!呵呵,谢谢了!

:victory: :victory: :victory: :victory: :victory:

楼主的box.net不能下了，好像说带宽用光了啊