| Introduction
In the
era of new health related technologies, Veterinary Medicine
is going to enter a phase of new and incredible transformations.
The major contributor to those changes is our recent ability
to measure, manipulate and organize matter at the nanoscale
level. Our understanding of the principles that rules the
nanoscale world is going to be of great impact on veterinary
research leading to new discoveries never before imagined.
Nanotechnology
has the potential to impact not only the way we live, but
also the way we practice veterinary medicine. Today scientists
foresee that the progress in the field of nanotechnology could
represent a major breakthrough in addressing some of our technical
challenges not only in engineering but also in the field of
both human and veterinary medicine. Very soon engineers would
develop tiny motors to power computers and appliances; and
doctors would have at their disposition miniature devices
that aim to fight cancer on the molecular level.
Veterinary
health care is a highly visible and growing concern not only
for pet’s owners, but also for our government. With an increasingly
aging pet population, along with higher costs for medications
and veterinary care, the need for new solutions is urgent.
At this period of time the main objective of Veterinary Medicine
is to excel, according to the accepted standards of scientific
excellence, in the creation of new knowledge and its translation
into improved health for the other species with which we share
or world, more effective veterinary services and products
and a strengthened veterinary education system.
For us
in the veterinary community, this article describes some of
the principal areas of nanotechnology currently being undertaken
in the world of medicine. Because the vast scope of the medical
applications of nanotechnology, this article is not intended
to be fully comprehensive nor cover every category of research.
The main purposes of this article are to trigger the interest
of discoveries of our profession in the field of very small
things and to provide a glimpse at potential important targets
for nanotechnology in the field of veterinary medicine. Also
it is important to mention that because nanotechnology is
at a very early stage of development, it may take several
years to perform the necessary research and conduct clinical
trials for obtaining meaningful results, but as professionals
we should begin to take notes.
Definitions
The most
widely use definition of nanotechnology is provided by the
United States Government’s National Nanotechnology Initiative.
According to them nanotechnology is defined as: “Research
and technology development at the atomic, molecular and macromolecular
levels at the scale of approximately 1 – 100 nanometer range,
to provide a fundamental understanding of phenomena and materials
at the nanoscale and to create and use structures, devices
and systems that have novel properties and functions because
of their small and / or intermediate size (1)”. A simple definition
of nanotechnology is the art of manipulating matter, atom
by atom. This new area of science can provide us with the
ability of assembling things from the atomic and molecular
blocks; the same way as today’s industry assembles cars in
factories from a set of predefined parts using robots. The
term nano is derived from the Greek word dwarf and is usually
combined with a noun to form words such as nanometer, nanobot
and nanotechnology. A nanometer is defined as one-billionth
of a meter. Since is not easy to visualize the scale of a
nanometer, a comparison with concepts and objects of appreciable
dimensions is helpful. To get a perspective of the scale used
in nanotechnology, representative structures and materials
found in nature are typically referenced to have the following
dimensions:
EXAMPLES
BIOLOGICAL STRUCTURES DIMENSION IN NANOMETERS
Leukocytes 10,000 nanometers
Bacteria 1,000 – 10,000 nanometers
Virus 75 – 100 nanometers
Protein 5-50 nanometers
DNA (with) 2 nanometers
Atom 0.1 nanometers
While
the word nanotechnology is increasing in popularity in the
scientific circles and the news; there is a word that since
the beginning has been associated with the development of
molecular manipulation. The term nanomedicine refers to the
use of molecular machine systems (i.e.: nanobots) to address
medical problems, and to the use of molecular knowledge to
maintain and improve health at a molecular scale (2). As a
specialized field within nanotechnology, nanomedicine would
work towards bodily repair through the use of engineered,
in vivo probes and sensors that would operate, in a semi-permanent
fashion, within the body. The development of nanomedicine
will have extraordinary implications for the veterinary profession,
because it will change the definition of disease and the way
we do diagnosis and treatment of medical conditions.
Nanomaterials
are structures created by nanotechnology research that range
from 1 to 100 nanometers in size. Common examples of nanomaterials
found in scientific literature are fullerenes, nanotubes,
buckyballs, quatum dots, dendrimers and nanoshells. Nanomaterials
can have very different properties than materials at the macro
scale. They can be stronger, lighter, more electrically conductive,
more porous and less corrosive than bulk materials. Nanomaterials
have the potential to solve unique biological challenges not
currently possible, such as having inorganic materials detect
electrical changes from biological molecules and react in
a manner that detects or treats a disease.
Fullerenes
are pure carbon molecules composed of at least 60 atoms of
carbon. Because a fullerenes takes a shape similar to a soccer
ball or a geodesic dome, it is sometimes referred as a buckyball
after the inventor of the geodesic dome, Buckminster Fuller,
for whom the fullerenes is normally named (3).
Nanotubes
are a sequence of nanoscale C60 atoms arranged in a long thin
cylindrical structure (4). They are related to two other carbon
crystal forms, graphite and diamonds. They are often described
as looking like rolls of graphite chicken wire, but as member
or the fullerene family; they are essentially buckyballs expanded
from the center into cylinders. Nanotubes are also called
buckytubes in some references books.
By definition,
Quantum dots is a nano-scale crystalline structure made from
cadmium selenide that absorbs white light and then reemits
it a couple of nanoseconds later in a specific color (5).
Dendrimers
are synthetic, three-dimensional macromolecule formed using
a nanoscale fabrication process (6). A dendrimer is built
up from a monomer, with new branches added in steps until
a tree-like structure is created. A dendrimer is technically
a polymer.
Nanoshells
are concentric sphere nanoparticles consisting of a dielectric
(typically gold sulfide or silica) core and a metal (gold)
shell (7). They are considered a very special kind of nanoparticles
because they combine infrared optical activity with the uniquely
biocompatible properties of gold colloid. In simple words,
they can be described as spherical glass particles with an
outer shell of gold. Their size is about 100 nanometers in
diameter.
Nanotechnology
can be viewed as a series of technologies that are used individually
or in combination to make products and applications, and to
better understand science (8). One way of characterizing nanotechnology
is by “tools”, “materials”, “devices” and “intelligent materials
or machines”. Nanotechnology tools include microscopy techniques
and equipment that permit the visualization and manipulation
of items at the nanoscale level such as cells, bacteria, viruses
and single molecules. The range of tools includes the atomic
force microscope, scanning tunneling microscope, molecular
modeling software and other technologies.
Nanotechnology
materials can be grouped into three main areas: raw materials,
nanostructured materials and the group composed by nanotubes
and fullerenes. The raw material includes nanoparticles and
nanocrystalline materials that are readily manufactured and
substitute less performing bulk materials. Nanostructured
materials are typically processed forms of raw material that
provide special shapes and functionality. Examples of nanostructured
materials include the quantum dots and the dendrimers. The
group of the nanotubes and fullerenes can produce materials
that are 100 times stronger than steel, more conductive than
copper, and can be safely used in some medical applications.
Two classes
of devices are commonly associated with nanotechnology. These
are the micro devices and nano devices. Examples of micro
devices are micro-electromechanical systems better know as
MEMS, microfluidics and microarrays. Even thought they are
not considered part of nanotechnology, these microtechnologies
have diverse medical applications. Nano devices are those
device technologies that are dimensioned at the nanoscale
level. Nano devices are difficult to produce at this moment,
but they are expected to have a brilliant future in the medical
field.
The intelligent
materials and machines are probably the most fascinating and
controversial area of nanotechnology. It includes the concept
of tiny artifacts, commonly known as nanobots or nanorobots,
which can be injected into the body to attack infections or
repair cells. So far, there are not serious research projects
in this area. Many decades may pass before this area may be
considered ready for commercialization.
Nanopharmaceuticals
One of
the areas of veterinary medicine that would benefit most from
the nanotechnology research is the field of pharmacology (9).
The creation and manipulation of new synthetic molecules can
provide us with new therapeutical compounds to treat diseases
in our pet population. These new compounds; for example, would
protect our patients from viral or bacterial infections and
accelerate wound healing. Also these new compounds could carry
drugs and genes into cells, making treatment of diseases more
efficacious.
One of
the most promising and productive areas of nanotechnology
are the nanopharmaceuticals. Most of our pet’s diseases one
day will be addressed by the use of nanopharmaceuticals (10).
Research in the area of nanopharmaceuticals would provide
new advances in the area of drug delivery systems. These systems
have an impact on the rate of absorption, distribution, metabolism,
and excretion of drugs or other substances in the body. They
must allow the drug to bind to its target receptor and influence
the receptor’s action. Drug delivery systems have severe restrictions
on the materials and production process that can be used.
The drug delivery material must be compatible and bind easy
with the drug, and be bioresorbable. The production process
must respect stringent conditions on processing and chemistry
that won’t degrade the drug, and still provide a cost effective
product.
One of
the major classes of drug delivery systems are materials that
encapsulate drugs to protect them during transit through the
body. When encapsulation materials are produced from nanoparticles
in the 1-to 100 nanometer size range instead of bigger micro
particles (commonly in use at this moment), they have a larger
surface area for the same volume, smaller pore size, improved
solubility, and different structural properties. This can
improve both the diffusion and degradation characteristics
of the encapsulation material.
Another
class of drug delivery systems are the nanomaterials that
can carry drugs to their destination sites and also have functional
properties. Certain nanostructures can be controlled to link
with a drug, a molecule or an imaging agent, then attract
specific cells and release their payload when required. Because
of their size, nanostructures have the ability to enter cells,
as cells will typically internalize materials below 100 nanometers.
Probably
the first trials to incorporate nanomaterials in the world
of medicine came from those studying the physical characteristics
and behavior of the buckyballs, a novel form of carbon discovered
by researchers many years ago. Some have compared buckyballs
to the discovery of benzene, another carbon molecule, from
which 40 percent of today drugs are made. The buckyballs are
only a nanometer long, perfectly smooth and round. They are
also inert, nontoxic and because of their size, they can interact
easily with cells, proteins and viruses. In addition, they
are hollow inside, so it is very easy to put pharmacological
agents inside them. Besides delivering medicine more efficiently
to the inside of cells, buckyballs may have a promising future
in the area of diagnostic imaging. It is feasible to put radioactive
agents inside the buckyballs so they can travel through the
bloodstream as the emit radiation (11). But since they are
excreted intact, they will completely remove the radiation
from the body after the procedure, reducing the complications
related to radiation toxicity.
Later
on scientists also have begun to look into the potential applications
of nanotubes as pharmacological agents. The antibacterial
properties of nanotubes are being studied; specifically the
ones designed by chemistry professor M. Reza Ghadiri and coworkers
at Scripps Research Institute. The nanotubes are formed by
self-assembled stacking of cyclic peptides having an even
number of alternating D- and L-aminoacids. The nanotubes insert
themselves readily into bacterial cell membranes and act as
potent and selective antibacterial agents, both in cell cultures
and in studies on mice (12). Both nanomaterials; buckyballs
and nanotubes, will undoubtedly become an important part of
the total pharmaceutical tool kit over the next few years.
Soybean
oil in its standard form has very few to none medical applications.
But once it is emulsified with detergents to form nanodrops
with measurements less than 600 nanometers, it can act as
a very potent destroyer of pathogens. Its mode of action is
not chemical, but a physical one. When the oil nanodrops contact
the membranes of bacteria or envelope viruses, the drops surface
tension forces a merger with the membrane, blowing it apart
and killing the pathogen. One very important characteristic
of the nanoemulsion is that they don’t affect cell structures
of higher organisms, which make it ideal to use in animals
and humans. While the nanoemulsion is entirely safe when applied
externally, unfortunately scientists had discovered that the
oil droplets can also destroy erythrocytes and sperm cells.
The reason seems to be that both types of cells lack the support
structures that make other cells invulnerable to the effects
of the nanodrops. This means that the nanoemulsion can’t be
use intravenously. If the research in the nanoemulsion continues
showing promising results, in the near future we may see bactericidal
and viricidal products that can be use topically in animals
and humans.
One of
the most important and promising areas of medical research
of today is the study of nanomaterials known as dendrimers.
They are synthetic polymers, a thousand times smaller than
cells. Dendrimers can be synthesized in various predetermined
sizes and can interact with biological agents by modifying
their surfaces properties. Three very important properties
of dendrimers make then an excellent candidate as pharmacological
agents. First, they can hold drug’s molecules in their structure
and serve as a delivery vehicle. Second, they can enter cells
very easy and release drugs right on target. Third and most
important, dendrimers don’t trigger immune system responses.
Dendrimers
have a lot to offer to the field of Veterinary Medicine. In
the future one of the major contributions of these synthetic
nanomaterials will be the diagnoses, treatment and eradication
of malignant tumors that commonly affect the small animal
geriatric population. They can serve as a drug delivery vehicle
for drugs or radioactive isotopes directly into a tumor microvasculature,
which may be considered as an alternative to direct irradiation
of tumors with fewer side effects. Medical researchers envisions
that one day dendrimers can execute a five step task when
dealing with the treatment of tumors: (i) dendrimers may be
able to find tumors cells through the body by looking for
tumor receptors, (ii) bind and pass through cell membranes,
(iii) perform a chemical analysis inside the cells to inform
veterinarians what type of tumors is present in the animal’s
body, (iv) release chemotherapy or radioactive agents inside
the tumor cells and (v) confirm via chemical analysis that
the procedure killed the cells. The same principles can one
day be applied to the treatment of hyperthyroid cats as an
example of how versatile these nanomaterials can be.
Besides
targeting tumor cells and drug delivery systems, dendrimers
has demonstrated promising results as tools for MRI imaging
(13-15) and gene transfer techniques (16). Also dendrimers
based nanocomposites are been studied as possible antimicrobial
agents against Staphylococcus aureus, Pseudomonas aeruginosa
and Escherichia coli.
Another
area that probably would benefit from the nanotechnology research
is the production of vaccines. The most recent studies indicate
that synthetic oligodeoxynucleotides and antigens in biodegradable
nanospheres can be use as an alternative approach for immunization
(17). A better immune response seems to be obtained with biodegradable
nanospheres that with vaccines produced by conventional methods.
Diagnostic
Tools
Nanotechnology
can bring to our veterinary hospitals cheaper, faster and
more precise diagnostic tools. Diagnostics test that usually
are sent to outside laboratories and can take from hours to
days to provide us with results may be considered as obsolete
sooner than we expected.
Quatum
dots particles are tiny crystals, which are a ten-millionth
of an inch in size. These particles enable powerful new approaches
to genetic analysis, drug discovery and disease diagnostics.
Today quantum dots are considered an important advancement
in our understanding of how genes work. Scientists believe
that in a couple of years this particles will be instrumental
in allowing researchers to monitor reactions of cells to certain
drugs or viruses.
Since
the beginning of last century researchers have used fluorescent
dyes to tag cells. These techniques however can problematic.
Each dye molecule requires a source of light of the same color
to cause it to illuminate. For instance, when using a green
dye, a source of light emitting the wavelength of the green
color is needed to be able to see the dye. The dyes are also
imprecise and have the tendency to blend together. They can
only be lit up for a short period of time, usually just a
few seconds after a light source is applied.
Instead
of depending of dyes, quantum dots technique offer the advantage
of that with only varying the size of the crystal you can
cause a rainbow of colors to fluoresce. The smaller the quantum
dots, the brighter the color. They stay lit for much longer
periods of time than dyes do, often for hours or days. Similar
to fluorescence, they allow us to tag different biological
components, like proteins or DNA strands, with specific colors.
For us in the veterinary profession, it means that quantum
dots could be used in a blood sample to quickly screen for
certain proteins that may indicate a higher propensity for
certain diseases.
To use
quantum dots as molecular labels, researchers coax the nanocrystals
into pores of tiny plastic beads that are tagged with a molecular
probe (a protein or DNA sequence) that bind strongly to the
molecule of interest. After the probe binds to its molecular
target in a cell or other biological sample, it is possible
to visualize the location or abundance of the molecule by
lighting up the dots with ultraviolet light. Current techniques
may allow researchers to create over 10,000 distinguishable
labels. With each label corresponding to a particular gene
or protein, researchers may be able to detect tens of molecules
all at once.
Some scientists
envision the possibility of injecting quatum dots into the
animal bodies. Once injected into the body they may detect
cells that are not working normally. Because they respond
to the effect of light, it may be possible to affect the behavior
of the dot once is inside the cell. For example, they may
be able to respond to a flash and heat up enough to destroy
cancerous cells.
Quantum
dots offer many technical advantages over traditional fluorescent
dyes, which are commonly used to detect and track biological
molecules. They not only can stay lit for a prolong period
of time, they are also brighter and easier to visualize than
organic dyes. They can be very helpful to visualize cell pathways,
which is essential for our understanding of how certain drugs
are going to behave in the animal’s body. In addition to their
usefulness in identifying and tracking molecules, they promise
faster, more flexible, and less costly tests for clinical
analysis.
Those
whom work in the veterinary field are familiar with immunoassay
testing. Immunoassay technology capitalizes on the characteristic
way that antibodies attach themselves to invading pathogens
in the body. Antibodies recognize and bind to antigens with
great specificity. One of the diagnostic applications of this
behavior exhibited by antibodies is the conventional immunoassay.
In a routine immunoassay test we expose a solution, such as
blood plasma for example, to a tray containing antibodies
that bind with a specific antigen under investigation. When
the antibodies bind to the antigen, the test changes color.
This system is used to identify and diagnose various conditions
that afflict the animal population.
Unfortunately,
we haven’t produced a fast and reliable whole blood immunoassay
yet, in part because blood is so viscous and murky that it
interferes with the chemical reactions in the test solution
and make it difficult to get accurate readings. Instead, clinicians
must purify the blood to remove these contaminants before
proceeding with the immunoassay, a time consuming step that
typically takes an hour or more. But nanotechnology research
may have found a way to overcome the problems with whole blood
immunoassays. Nanotechnology researchers have developed a
new method of testing whole blood using optically active gold-coated
glass particles commonly known as gold nanoshells (18).
In laboratory
tests, the nanoshells immunoassay was capable of detecting
less than one billionth of a gram of IgG per milliliter of
whole blood. This may be the first whole-blood immunoassay
to report sensitivities on this order under 30 minutes. The
nanoshells immunoassay overcome the obstacles commonly attributed
to whole-blood immunoassay coupling antibodies to nanoshells
that absorb near-infrared light. Nanoshells are layered colloids
that consist of a core of non-conducting material covered
by a thin metallic shell. By varying the thickness of the
metal shell, researchers can precisely tune the color of light
to which the nanoshells respond. Because near infrared light
penetrates whole blood very well, it is an optimal wavelength
for a whole blood immunoassay. When the antibody-nanoshells
particles are placed into a solution of whole blood containing
the test molecule, the antibody-nanoshells bind to the test
molecule, which causes slight changes in the optical properties
of the nanoshells. By monitoring these changes, researchers
are able to monitor very slight concentrations of antigens
in the blood, without any time-consuming sample preparation.
Nanoshells
are also been tested as a noninvasive way to detect tumors.
Since they are gold coated, nanoshells would not trigger an
immunity response. Scientists had found that they can attach
to the shells antibodies that would lock onto specific tumor
cells. This nanoshells are then injected into the body of
a laboratory animal, turned on a light source (a laser or
infrared light for examples) and observe if and where the
nanoshells accumulates. But nanoshells are more than a marker,
it turn out. It has been found that they could be use to destroy
tumors as well (19). Like a magnifying glass, nanoshells concentrate
light beamed at them and heat up. Their studies showed the
shells killed tumor cells without harming skin or nearby healthy
tissue. While more studies with this novel optical materials
need to be done, we can said today that nanoshells will play
an important role in the future of veterinary care.
Conclusions
Clearly,
the profession of Veterinary Medicine will be substantially
different in 25 years from that of today. It can be hope that
nanotechnology, in addition to contribute to the creation
of changes in our profession, will also be one of the technologies
that help practitioners stay abreast of and manage these developments.
Because nanotechnology is not in the mainstream quite yet,
most of us in the veterinary community are simply unaware
of it’s potential. In order to appreciate the advantages of
this technology, the veterinary profession needs to understand
it’s basic concepts and contributions. This may require that
everyone involve in our profession spend some time educating
themselves. The best way to begin is trying to understand
the definitions of nanotechnology, nanomedicine, etc…. Whatever
our specialty is, we should ask ourselves the following questions:
If I could do this at a molecular level, how would things
be changed? As a group we need to coordinate efforts to create
a generation of veterinarians that will understand nanotechnology.
We as
an organized profession should have some influence in public
policies about nanotechnology and other new fields or research.
Our profession needs to be more vocal about issues new technologies
such as cloning and stem cell research. It is responsibility
of the veterinary community to maintain awareness of these
technologies and the benefits they can bring to our patients.
One way we can prepare our profession for changes due to new
technologies is to advice the academia and commercial organizations
about our needs. Support to those involved in new technological
research such as nanotechnology is very important. Despite
initial success, the veterinary applications of nanotechnology
are in its infancy, and a number of hurdles remain prior to
bringing these therapies into the clinical arena. Encouraging
commercial organizations to make good and useful products
based on this technology can be crucial for the ultimate benefit
of our profession. The real challenge to veterinary medicine
is to understand and apply these technologies in a way that
will provide maximum benefits to our patient’s health. I am
confident that once our colleagues and clients begin to realize
the great benefits of nanotechnology, especially in terms
of pet healthcare, there will be no problem generating the
enthusiasm needed to make nanotechnology an important and
vital tool for the enhancement of our profession. Nanotechnology
will raise our technological capabilities to a new level,
improving pet health care and quality of life. It will also
increase our standard of living and it will drive futher economic
expansion into the veterinary profession. We as member of
the veterinary community have an unique opportunity to become
major players in the development of nanotechnological applications
in the fields of animal and human medicine. We need to create
significant momentum while the field still emerging to later
recollect the fruits of our actions.
References
(1) Nanotechnology
definition: National Nanotechnology Initiative. February 2000.
http://www.nano.gov/omb_nifty50htm
(2) Freitas,
Robert A., Nanomedicine, Volume I: Basic Capabilities, Landes
Bioscience, Georgetown, Texas.1999.
(3) Fullerenes
definition: http://whatis.techtarget.com/definition/0,,sid9_gci2145
(4) Nanotubes
definition: http://www.webopedia.com/TERM/N/nanotube.html
(5) Quantum
dot definition: http://www.webopedia.com/TERM/Q/quantum_dot.html
(6) Dendrimer
definition: http://www.webopedia.com/TERM/D/dendrimer.html
(7) Avaritt
R. D. et al.: Plasmon resonance shifts of Au-coated Au 25
nanoshells: insight into multicomponent nanoparticle growth.
Phys Rev Lett. 78: 4217-20. 1997.
(8) Gordon,
N.; Sagman, U.: Nanomedicine taxonomy: briefing paper. Canadian
Nanobusiness Alliance. February 2003. http://www.regenerativemedicine.ca/nanomed/NanomedicineTaxonomy
(9) Feneque,
J.: Nanotechnology: a new challenge for veterinary medicine.
The Pet Tribune. 6 (5): 16. 2000.
(10) Feneque,
J.: The future of nanopharmaceuticals in veterinary medicine.
http://nanotech-now.com/Nanopharmaceuticals-and-Veterinary-Medicine.ht
(11) Wilson, L. J.: Medical applications of fullerenes and
metallofullerenes.
Interface. 8: 24-28. 1999.
(12)
Fernandez-Lopez, S.; et al: Antibacterial agents based on
the cyclic D-, L- alpha
peptide architecture. Nature. (412): 452-455. (26 Jul 2001).
(13)
Wu, C.; et al. Bioorganic And Medicinal Chemistry Letters.
4(3): 449. 1994.
(14)
Margerum, L.D.; et al. J Alloys Comp. 249 (1-2): 185. 1997.
(15)
Kim, Y.; Zimmerman, S.C.: Curr Opin Chem Biol. 2(6): 733-742.
1998.
(16)
Balogh, L.; et al. Dendrimer nanocomposites in medicine. Chimica
Oggi.
20 (5): 35. May 2002.
(17)
Diwan, M.; et al. Enhancement of immune responses by co-delivery
of A CpG
oligodeoxynucleotide and tetanus toxoid in biodegradable nanospheres.
J Control
Release. 85(1-3): 247-62. Dec 13, 2002.
(18)
L. R. Hirsch; et al. A whole blood immunoassay using gold
nanoshells.
Analytical Chemistry. 75 (10): 2377- 2381. 2003.
(19)
L.R. Hirsch; et al. Nanoshell mediated near infrared photo
dermal tumor
therapy. Summer Bioengineering Conference, Key Biscayne, Florida.
2003
http://www.tulane.edu/~sbc2003/pdfdocs/0751.PDF
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