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Posts Tagged ‘Bioanalytical Chemistry’


Laser-induced breakdown spectroscopy (LIBS) for bioscience investigation

Curator: Larry H. Bernstein, MD, FCAP

LPBI

 

 

Biological Mapping with LIBS

By Laura Bush

Spectroscopy Apr 01, 2016; 31(4):26–31

 

Vincent Motto-Ros of Lyon 1 University, in Lyon, France, is combining the ability of atomic spectroscopy techniques to detect and quantify metals with the mapping approaches most often used with molecular techniques. He has combined laser-induced breakdown spectroscopy (LIBS) with electron microscopy to map the metals and metallic nanoparticles in biological tissue, as a way of studying the update and clearance of these materials by biological systems. In this interview, he discusses his work applying LIBS to biological analysis, including the methods, advantages, and future directions.

In recent years, many researchers have been advancing the application of molecular spectroscopy techniques, such as Raman and infrared (IR) spectroscopy, to image biological tissues, such as for the analysis of tumors. Atomic spectroscopy techniques such as inductively coupled plasma-mass spectrometry (ICP-MS), on the other hand, are being used extensively to study metals and metallic nanoparticles in biological matrices. Vincent Motto-Ros of the Light and Matter Institute at Lyon 1 University, in Lyon, France, is combining the ability of atomic techniques to detect and quantify metals with the scanning approaches most often used with molecular techniques. He has used laser-induced breakdown spectroscopy (LIBS) to image metals and metallic nanoparticles in biological tissue, as a way of studying the uptake and clearance of these materials by biological systems. He recently spoke to us about this work.

You are developing LIBS techniques for the imaging analysis of metallic nanoparticles and other metals in biological tissue. How does LIBS imaging work?

In LIBS imaging, laser-induced plasma are generated continuously while scanning the sample surface over the region of interest. Elemental images are obtained, in a pixel-by-pixel manner, after extracting the intensity of the interesting species (atoms, ions, or molecules) from each recorded spectrum (Figure 1).

Figure 1: (a) Principle of LIBS imaging instrument with the major components, including the microscope objective used to focus the UV laser pulse, the motorized platform supporting the sample, and the optical detection system fiber-connected to the spectrometer. (b) Example of single-shot emission spectra in the 315–345 nm spectral range recorded in three different regions of the mouse kidney sample indicated in (a) with emission lines of calcium (Ca), sodium (Na), and gadolinium (Gd). (c) Relative-abundance images of Gd (green), Ca (yellow), and Na (red) represented in a false color scale. (d) Multielemental biodistributions in a coronal murine kidney section, 24 h after Gd-based nanoparticle administration (spatial resolution of 10 µm).

 

In a recent study in mice, you used LIBS to investigate the renal clearance of gadolinium-based nanoparticles that are being studied for their potential as both diagnostic tools and therapeutics (1). What exactly were you looking for?

Nanomaterials represent a huge potential for future medical applications, but the characterization of these attractive candidates within biological tissue remains very challenging, especially because of their small size. Any modification applied to such small nanoparticles, such as fluorescence labeling, may indeed modify their shape, size, or charge, and therefore affect their biodistribution. In this work, we wanted to study the renal biodistribution of gadolinium-based nanoparticles with the aim to show the potential of LIBS for label-free imaging of nanoparticles, and metals more generally, in their biological environment.

What benefits can LIBS offer for such studies compared to existing elemental methods?

The LIBS approach is the only optical technique able to image elements with parts-per-million sensitivity and a resolution in the range of a few micrometers. The simplicity of the setup endows LIBS with a series of advantages including an all-optical design compatible with standard optical microscopy, reduced cost, and operation in ambient atmosphere. In addition, although LIBS is not as sensitive as laser-ablation ICP-MS (LA-ICP-MS), which has a sensitivity of
< 500 ppb, or as high-resolving as micro X-ray fluorescence spectrometry (< 1 µm), it has a fast operating speed, which can be up to 100 times faster than other techniques. These advantages enable LIBS imaging to provide large-scale images over entire organs (> 1 cm²) with a cellular scale resolution (~10 µm) and in reasonable time periods.

How did you optimize the balance between spatial resolution and detection sensitivity?
Achieving an adequate balance between spatial resolution and detection sensitivity is indeed one of the critical points for setting up a LIBS imaging instrument. In LIBS, sensitivity and the resolution are tightly linked. Resolution is governed by the size of the ablation craters, whereas sensitivity relies on the amount of vaporized material and on the excitation capability of the laser pulse. For example, improving the resolution (using for example an objective with a higher magnification) may dramatically lower the sensitivity. Considering our given experimental configuration (UV laser pulse, x15 magnification objective, collection system, and so on) the best performance, both in terms of signal-to-noise ratio and crater size, was obtained for a pulse energy of 800 µJ.

In this study, the kidney samples were embedded in epoxy before analysis. Would it be possible to do this kind of analysis on fresh tissue?

Yes, our first studies were carried out on fresh tissue slices (2,3). However, mastering the laser ablation of such soft materials is difficult and the accessible resolution is quite poor (~100 µm). The use of epoxy-embedded samples offers better ablation control compared with fresh tissue, which greatly improves the sample’s mechanical stability, the ablation shot-to-shot repeatability, and thus the accessible resolution.

How were the elements of interest quantified using the imaging technique?

A standard quantification methodology was used. Standards were made in epoxy resin with graduated concentration of the elements of interest (Gd, Si, Na, Fe). Calibration curves were then built for each element and the relative-abundance images were subsequently transformed into quantitative-abundance images.

What limits of detection were you able to attain for the various elements you measured?

We typically obtained detection limits of 10 ppm for Gd, 2 ppm for Si, and 5 ppm for Na, values estimated from single-shot measurements.

What were the initial results in this study, particularly as you studied the renal clearance of the nanoparticles over time?

These LIBS experiments made it possible to image the components of the nanoparticles (Gd and Si) throughout the entire kidney and provided evidence of both their rapid renal uptake and their elimination. We also imaged elements naturally present in the tissue such as Na, Ca, Fe, Cu, P, and Mg. The kinetics of nanoparticle elimination was evaluated from kidney samples collected at various times after nanoparticle administration (Figure 2). These results highlight the appropriate elimination of nanoparticles from the organism, which is a fundamental necessity for the clinical development of such agents.

Figure 2: Quantitative imaging of Gd and Na in kidney coronal sections showing the fast renal uptake and elimination of nanoparticles. Mouse kidney samples were collected at various times after nanoparticle administration (ranging from 5 min to 1 week).

 

Overall, what did your study show about the suitability of LIBS to this type of work?

The LIBS imaging capability is very complementary to conventional methods for biological research, such as transmission electron microscopy or immunohistochemistry. Importantly, this work has drawn the attention of biologists working in the field of nanotechnology. They are seeing in LIBS a promising approach for preclinical studies with the idea to provide the biodistribution of nanomaterials at the scale of an entire organ. Since doing this study, we have worked on several applications where LIBS imaging has been used among other techniques to evaluate the biological activity and toxicity of various types of nanoparticles (4–6).

How large an area did you sample, and how long did it take? How feasible is this method for mapping larger samples?

Imaging large areas by LIBS is not technically difficult as long as the sample is perfectly flat (or alternatively the instrument has to be equipped with an autofocus system). The scanning speed is critical, however, because recording high-definition images with a large number of pixels can take a considerable amount of time. All the images shown above were obtained using an instrumentation operating at 10 Hz. With this acquisition rate, 36,000 pixels were recorded within 1 h. This year, we updated our instruments to increase the scanning rate to 100 Hz. This obviously provides more comfortable conditions for analyzing larger samples. An example is shown in Figure 3. This image of 500,000 pixels represents a rat kidney section (~2 cm²) and was recorded in about 80 min at 100 Hz.

Figure 3: High-definition image showing the biodistribution of gold-based nanoparticles in a rat kidney. This image of around 500,000 pixels was recorded with a resolution of 20 µm and covers a surface of about 2 cm².

 

What are your next steps in this work?

As already mentioned, we are working on the improvement of the acquisition rate. We should be able to make our first kilohertz tests in a couple of weeks. In addition, we are also investigating the three-dimensional capability of the technique with the aim both to provide a global organ distribution of metals and to focus on specific regions of the tissue with cellular-scale resolution. At the present time, we are also working on samples with more complex architectures such as the brain, lungs, or tumors, and with other types of metal-based nanoparticles (gold, silver, platinum, and so on).

References

  1. L. Sancey, V. Motto-Ros, B. Busser, S. Kotb, J.M. Benoit, A. Piednoir, F. Lux, O. Tillement, G. Panczer, and J. Yu, Scientific Reports 4, 6065 (2014).
  2. V. Motto-Ros et al., Spectrochim. Acta, Part B 83, 168–174 (2013).
  3. V. Motto-Ros et al., Appl. Phys. Lett. 101, 223702 (2012).
  4. L. Sancey et al., ACS Nano 9, 2477 (2015).
  5. A. Moussaron et al., Small 11, 4900 (2015).
  6. S. Kunjachan et al., Nano Letters 15, 7488 (2015).

 

Vincent Motto-Ros is an associate professor at the Light and Matter Institute at Lyon 1 University, in Lyon, France.

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DNA Repair

Larry H. Bernstein, MD, FCAP, Curator

LPBI

 

Chemical Communications Blog

In celebration of the 2015 Nobel Prize in Chemistry

http://blogs.rsc.org/cc/2015/10/27/in-celebration-of-the-2015-nobel-prize-in-chemistry/

The 2015 Nobel Prize in Chemistry was jointly awarded to Tomas Lindahl, Paul Modrich and Aziz Sancar for their “mechanistic studies of DNA repair”. Their research has not only revolutionised our knowledge of how we function but it also lead to the development of life-saving treatments. In celebration of their landmark achievements, we are delighted to present a special Nobel Prize collection of recent Chemical Communications, Chemical Science and Chemical Society Reviews articles on DNA repair.
2015 Nobel Prize in Chemistry winners
Tomas Lindahl, Paul Modrich and Aziz Sancar © Inserm-P. Latron, Mary Schwalm/AP/Press Association, Max Englund/UNC School of Medicine.
Thomas Lindahl’s research pieced together a molecular image of how base excision repairs DNA when a base of a nucleotide is damaged and subsequently managed to recreate the human repair process in vitro. The mechanism known as nucleotide excision repair, which excises damage from UV and carcinogenic substances, was then mapped by Aziz Sancar – the molecular details of this process changed the entire research field. Paul Modrich also studied the human version of the repair system. His work focused on DNA mismatch repair, a natural process which corrects mismatches that occur when DNA is copied during cell division.
The research carried out by the three 2015 Nobel Laureates in Chemistry has not only revolutionised our knowledge of how we function but also lead to the development of life – saving treatments.

Reviews

Finding needles in a basestack: recognition of mismatched base pairs in DNA by small molecules
Anton Granzhan, Naoko Kotera and  Marie-Paule Teulade-Fichou
Chem. Soc. Rev., 2014, 43, 3630-3665
DOI: http://dx.doi.org:/10.1039/C3CS60455


The chemical biology of sirtuins
Bing Chen, Wenwen Zang, Juan Wang, Yajun Huang, Yanhua He,  Lingling Yan,  Jiajia Liu and Weiping Zheng
Chem. Soc. Rev., 2015, 44, 5246-5264
DOI: http://dx.doi.org:/10.1039/C4CS00373J


Luminescent oligonucleotide-based detection of enzymes involved with DNA repair
Chung-Hang Leung, Hai-Jing Zhong, Hong-Zhang He, Lihua Lu, Daniel Shiu-Hin Chan and Dik-Lung Ma
Chem. Sci., 2013, 4, 3781-3795
DOI: http://dx.doi.org:/10.1039/C3SC51228B


 

 

Research articles

A label-free and sensitive fluorescent method for the detection of uracil-DNA glycosylase activity
Jing Tao, Panshu Song, Yusuke Sato, Seiichi Nishizawa, Norio Teramae, Aijun Tong  and Yu Xiang
Chem. Commun., 2015, 51, 929-932
DOI: http://dx.doi.org:/10.1039/C4CC06170E


DNA-mediated supercharged fluorescent protein/graphene oxide interaction for label-free fluorescence assay of base excision repair enzyme activity
Zhen Wang, Yong Li, Lijun Li, Daiqi Li, Yan Huang, Zhou Nie and Shouzhuo Yao
Chem. Commun., 2015, 51, 13373-13376
DOI: http://dx.doi.org:/10.1039/C5CC04759E


A fluorescent G-quadruplex probe for the assay of base excision repair enzyme activity
Chang Yeol Lee, Ki Soo Park and Hyun Gyu Park
Chem. Commun., 2015, 51, 13744-13747
DOI: http://dx.doi.org:/10.1039/C5CC05010C


A chemical probe targets DNA 5-formylcytosine sites and inhibits TDG excision, polymerases bypass, and gene expression
Liang Xu, Ying-Chu Chen, Satoshi Nakajima, Jenny Chong, Lanfeng Wang,  Li Lan, Chao Zhang and  Dong Wang
Chem. Sci., 2014, 5, 567-574
DOI: http://dx.doi.org:/10.1039/C3SC51849C


Sensitive detection of polynucleotide kinase using rolling circle amplification-induced chemiluminescence
Wei Tang, Guichi Zhu and Chun-yang Zhang
Chem. Commun., 2014, 50, 4733-4735
DOI: 10.1039/C4CC00256C


Rescuing DNA repair activity by rewiring the H-atom transfer pathway in the radical SAM enzyme, spore photoproduct lyase
Alhosna Benjdia, Korbinian Heil, Andreas Winkler, Thomas Carell and Ilme Schlichting
Chem. Commun., 2014, 50, 14201-14204
DOI: http://dx.doi.org:/10.1039/C4CC05158K


Expanding DNAzyme functionality through enzyme cascades with applications in single nucleotide repair and tunable DNA-directedassembly of nanomaterials
Yu Xiang, Zidong Wang, Hang Xing and  Yi Lu
Chem. Sci., 2013, 4, 398-404
DOI: http://dx.doi.org:/10.1039/C2SC20763J


Detection of base excision repair enzyme activity using a luminescent G-quadruplex selective switch-on probe
Ka-Ho Leung, Hong-Zhang He, Victor Pui-Yan Ma, Hai-Jing Zhong, Daniel Shiu-Hin Chan,  Jun Zhou,  Jean-Louis Mergny, Chung-Hang Leung and  Dik-Lung Ma
Chem. Commun., 2013, 49, 5630-5632
DOI: http://dx.doi.org:/10.1039/C3CC41129J


Endonuclease IV discriminates mismatches next to the apurinic/apyrimidinic site in DNA strands: constructing DNA sensing platforms with extremely high selectivity
Xianjin Xiao, Yang Liu and  Meiping Zhao
Chem. Commun., 2013, 49, 2819-2821
DOI: http://dx.doi.org:/10.1039/C3CC40902C

 

 

Top 15 most downloaded Chem Soc Rev articles in Q3, 2015

Ultra-stable organic fluorophores for single-molecule research
Qinsi Zheng, Manuel F. Juette, Steffen Jockusch, Michael R. Wasserman, Zhou Zhou, Roger B. Altman and Scott C. Blanchard
DOI: 10.1039/C3CS60237K, Review Article

The chemistry of graphene oxide
Daniel R. Dreyer, Sungjin Park, Christopher W. Bielawski and Rodney S. Ruoff
DOI: 10.1039/B917103G, Critical Review

Selection of boron reagents for Suzuki–Miyaura coupling
Alastair J. J. Lennox and Guy C. Lloyd-Jones
DOI: 10.1039/C3CS60197H, Review Article

Physical and chemical tuning of two-dimensional transition metal dichalcogenides
Haotian Wang, Hongtao Yuan, Seung Sae Hong, Yanbin Li and Yi Cui
DOI: 10.1039/C4CS00287C, Review Article

Advances on structuring, integration and magnetic characterization of molecular nanomagnets on surfaces and devices
N. Domingo, E. Bellido and D. Ruiz-Molina
DOI: 10.1039/C1CS15096K, Critical Review

Heterogeneous photocatalyst materials for water splitting
Akihiko Kudo and Yugo Miseki
DOI: 10.1039/B800489G, Critical Review

Shape control in gold nanoparticle synthesis
Marek Grzelczak, Jorge Pérez-Juste, Paul Mulvaney and Luis M. Liz-Marzán
DOI: 10.1039/B711490G, Tutorial Review

An overview of nanoparticles commonly used in fluorescent bioimaging
Otto S. Wolfbeis
DOI: 10.1039/C4CS00392F, Review Article

Heterogeneous catalysis for sustainable biodiesel production via esterification and transesterification
Adam F. Lee, James A. Bennett, Jinesh C. Manayil and Karen Wilson
DOI: 10.1039/C4CS00189C, Review Article

A review of electrode materials for electrochemical supercapacitors
Guoping Wang, Lei Zhang and Jiujun Zhang
DOI: 10.1039/C1CS15060J, Critical Review

MOF positioning technology and device fabrication
Paolo Falcaro, Raffaele Ricco, Cara M. Doherty, Kang Liang, Anita J. Hill and Mark J. Styles
DOI: 10.1039/C4CS00089G, Review Article

Microfluidic lab-on-a-chip platforms: requirements, characteristics and applications
Daniel Mark, Stefan Haeberle, Günter Roth, Felix von Stetten and Roland Zengerle
DOI: 10.1039/B820557B, Critical Review

Noble metal-free hydrogen evolution catalysts for water splitting
Xiaoxin Zou and Yu Zhang
DOI: 10.1039/C4CS00448E, Review Article

“Green” electronics: biodegradable and biocompatible materials and devices for sustainable future
Mihai Irimia-Vladu
DOI: 10.1039/C3CS60235D, Review Article

Synthetic biology for the directed evolution of protein biocatalysts: navigating sequence space intelligently
Andrew Currin, Neil Swainston, Philip J. Day and Douglas B. Kell
DOI: 10.1039/C4CS00351A, Review Article

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Heroes in Basic Medical Research – Leroy Hood

Larry H Bernstein, MD, FCAP, Curator

Leaders in Pharmaceutical Intelligence

Series E. 2; 4.5

Leroy Hood, MD, PhD

Dr. Hood created the technological foundation for the sciences of genomics (study of genes) and proteomics (study of proteins) through the invention of five groundbreaking instruments and by explicating the potentialities of genome and proteome research into the future through his pioneering of the fields of systems biology and systems medicine. Hood’s instruments not only pioneered the deciphering of biological information, but also introduced the concept of high throughput data accumulation through automation and parallelization of the protein and DNA chemistries.

The first four instruments were commercialized by Applied Biosystems, Inc., a company founded by Dr. Hood in 1981, and the ink-jet technology was commercialized by Agilent Technologies, thus making these instruments immediately available to the world-community of scientists.

The first two instruments transformed the field of proteomics. The protein sequencer allowed scientists to read and analyze proteins that had not previously been accessible, resulting in the characterization of a series of new proteins whose genes could then be cloned and analyzed. These discoveries led to significant ramifications for biology, medicine, and pharmacology. The second instrument, the protein synthesizer, synthesized proteins and peptides in sufficient quantities to begin characterizing their functions. The DNA synthesizer, the first of three instruments for genomic analyses, was used to synthesize DNA fragments for DNA mapping and gene cloning. The most notable of Hood’s inventions, the automated DNA sequencer developed in 1986, made possible high-speed sequencing of human genomes and was the key technology enabling the Human Genome Project.

In the early 1990s Hood and his colleagues developed the ink-jet DNA synthesis technology for creating DNA arrays with tens of thousands of gene fragments, one of the first of the so-called DNA chips, which enabled measuring the levels of 10,000s of expressed genes. This instrument has also transformed genomics, biology, and medicine.

In 1992, Hood created the first cross-disciplinary biology department, Molecular Biotechnology, at the University of Washington. In 2000, he left the UW to co-found Institute for Systems Biology, the first of its kind. He has pioneered systems medicine the years since ISB’s founding.

In 2000, Hood and two colleagues founded the Institute for Systems Biology (ISB), a nonprofit research institute integrating biology, technology, computation and medicine to take a systems (holistic) approach to studying the complexity of biology and medicine by analyzing all elements in a biological system rather than studying them one gene or protein at a time (an atomistic approach).

Hood has made many seminal discoveries in the fields of immunology, neurobiology and biotechnology and, most recently, has been a leader in the development of systems biology, its applications to cancer, neurodegenerative disease, and the linkage of systems biology to personalized medicine.

Hood’s efforts in a systems approach to disease have led him to pioneer a new approach to medicine that he coined P4 Medicine in 2003. His view is that P4 medicine will transform the practice of medicine over the next decade, moving it from a largely reactive discipline to a proactive one.

Dr. Hood’s outstanding contributions have had a resounding effect on the advancement of science since the 1960s. Throughout his career, he has adhered to the advice of his mentor, Dr. William J. Dreyer: “If you want to practice biology, do it on the leading edge, and if you want to be on the leading edge, invent new tools for deciphering biological information.”

 

Hood is now pioneering new approaches to P4 medicine

Co-founder and Chairman P4 Medicine institute

—predictive, preventive, personalized and participatory, and most recently, has embarked on creating a P4 pilot project on 100,000 well individuals, that is transforming healthcare.

In addition to his ground-breaking research, Hood has published 750 papers, received 36 patents, 17 honorary degrees and more than 100 awards and honors. He is one of only 15 individuals elected to all three National Academies—the National Academy of Science, the National Academy of Engineering, and the Institute of Medicine. Hood has founded or co-founded 15 different biotechnology companies.

 

http://www.youtube.com/watch%3Fv%3D5aE8tgbsl9U Feb 18, 2015 Dr. Leroy Hood, President and Co-founder, Institute for Systems Biology, gives a talk entitled “Systems Medicine and a Longitudinal, …

http://www.youtube.com/watch%3Fv%3DaYGTLj02sx0  Nov 19, 2014 … of Healthcare? A Personal View of Biological Complexity, Paradigm Changes, Systems Biology and Systems Medicine .Speaker: Leroy Hood.

http://www.youtube.com/watch%3Fv%3DnT1MvnH6j8Q Sep 26, 2014 Dr. Leroy Hood discusses how P4 (Predictive, Preventive, … EMBC 2014 Theme Keynote Lecture with Dr. Emery Brown – Duration: 58:49. by …

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Analysis of S-nitrosylated Proteins: Detergent-free biotin switch combined with liquid chromatography/tandem mass spectrometry

Author and Curator: Larry H Bernstein, MD, FACP 

 

Detergent-free biotin switch combined with liquid chromatography/tandem mass spectrometry in the analysis of S-nitrosylated proteins.

Han P; Chen C
National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China.
Rapid Commun Mass Spectrom. 2008 Apr; 22(8):1137-45.   http://dx.doi.org/10.1002/rcm.3476.    PMID: 18335467

 

High-throughput proteomic analysis based on a biotin switch combined with liquid chromatography/tandem mass spectrometry (LC/MS/MS)

  • enables simultaneous identification of S-nitrosylated sites and
  • their cognate proteins in complex biological mixtures, which is a great help
    • in elucidating the functions and mechanisms of this redox-based post-translational modification.

However, detergents such as sodium dodecyl sulfate (SDS) and Triton X-100 adopted in these systems, which are hard to fully remove in the subsequent MS-based analyses,

  1. can suppress the peptide signals and
  2. influence the SNO-Cys site identification and
  3. the reproducibility of the experiments.

Here we developed a detergent-free biotin-switch method, which applied

  1. urea to replace detergents, and successfully
  2. combined it with LC/MS/MS in the analysis of S-nitrosylated proteins.

With this approach, 44 SNO-Cys sites were specified on 35 distinct proteins in S-nitrosoglutathione (GSNO)-treated HeLa cell extracts of proteins with good reproducibility.

The LC/MS performance was greatly improved as

  • analyzed with Pep3D and the amount of samples for analysis reduced from 40 mg used in the literature to 3-5 mg.

For S-nitrosylated targets detected both in the control sample and in the GSNO-treated sample,

  • extracted ion chromatography (XIC) was employed to
  • estimate the quantitative change of S-nitrosylation (S-nitrosation),

which facilitates the judgment on ‘accept or reject’ of the identified targets.

 

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Computationally designed “self”-peptide could be used to better target drugs to tumors, to ensure pacemakers are not rejected, and to enhance medical imaging technologies

Reporter: Aviva Lev-Ari, PhD, RN

Synthetic Peptide Fools Immune System

Researchers have created a molecule that helps nanoparticles evade immune attack and could improve drug delivery.

By Dan Cossins | February 21, 2013

 

A macrophage at work in a mouse, stretching itself to gobble up two smaller particlesFLICKR, MAGNARAMA synthetic molecule attached to nanoparticles acts like a passport, convincing immune cells to let the particles pass unimpeded through the body, according to a study published today (February 21) in Science. The computationally designed “self”-peptide could be used to better target drugs to tumors, to ensure pacemakers are not rejected, and to enhance medical imaging technologies.

“It’s the first molecule that can be attached to anything to attenuate the innate immune system, which is currently limiting us from delivering therapeutic particles and implanting devices,” saidDennis Discher, a professor of biophysical engineering at the University of Pennsylvania and a coauthor of the study.

“This is really interesting work,” said Joseph DeSimone, a chemical engineer at the University of North Carolina, Chapel Hill, who was not involved in the research, in an e-mail to The Scientist. “[It] strongly validates the idea of using biological evasion strategies.”

Macrophages recognize, engulf, and clear out foreign invaders, whether they’re microbes entering through a wound or a drug-loaded nanoparticle injected to target disease. Previously, researchers have attempted to escape this response by coating nanoparticles with polymer “brushes” to physically block the adhesion of blood proteins that alert macrophages to the particles’ presence. But these brushes can only delay the macrophage-signaling proteins for so long, and they can hinder uptake by the diseased cells being targeted.

With that in mind, Discher and colleagues tried instead to find a way to convince macrophages that nanoparticles are part of the body. Their previous research had shown that a membrane protein called CD47, which binds to macrophages in humans, signals “self” to the immune system, so that particles with this protein are not attacked.

Examining the architecture of the bond between CD47 and its macrophage receptor, SIRPα, the researchers were able to design a synthetic self-peptide with a similarly snug fit. “This is the key, literally, to unlocking innate immune pacification,” said Discher.

When they chemically synthesized the 21-amino-acid self-peptide and attached it to nanobeads as small as viruses in mice genetically engineered to have human-like SIRPα receptors, the researchers showed that beads with the self-peptide stayed in the blood of for longer than beads with no peptide: 30 minutes after being injected with equal numbers of each type, there were 4 times as many beads with the peptide attached than without. The results demonstrate that the synthetic molecule can reduce the rate at which phagocytes clear the beads from the body, said Discher.

Then, in mice with human lung cancer, the researchers injected fluorescently dyed beads with and without the peptide, and saw that the “self”-beads got through the macrophage-filled spleen and liver and accumulated in greater numbers in the tumor, providing a brighter signal under when imaged. In fact, the self-beads provided a signal from the tumor as strong as beads coated with human CD47.

Finally, to see whether the biological evasion strategy can be successfully combined with targeting, the researchers loaded an anticancer drug into self-beads also coated with antibodies that target cancer cells. Sure enough, these antibody-coated self-beads consistently shrank tumors more than antibody-coated beads lacking the peptide. This confirmed that when antibodies draw the attention of the macrophage, the self-peptides inhibit the macrophage’s response, acting as a “don’t-eat-me” signal, said Discher.

The results demonstrate that the synthetic peptide can provide therapeutic nanoparticles with extra time in the body—time that improves drug delivery. Furthermore, the relative simplicity of the peptide means it can be easily synthesized, making it an attractive component for use in a variety of future applications.

“The findings are “compelling” and “the technology merits moving forward,” Omid Farokhzad, director of the Laboratory of Nanomedicine and Biomaterials at Brigham and Women’s Hospital, part of Harvard Medical School, said in an e-mail to The Scientist.

A crucial next step is to test the efficacy of synthetic self-peptides in humans, Farokhzad added. “The truly relevant test is looking at human pharmacokinetics to see circulating half-life advantages of nanoparticles and their effect on therapeutic outcome.”

P.L. Rodriguez et al., “Minimal ‘self’ peptides that inhibit phagocytic clearance and enhance delivery of nanoparticles,” Science, 339: 971-74, 2013.

SOURCE

 

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