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use of minor species for the benefits of mankind always has
been a controversial topic in modern society. Especially the
use of animals for medical research, which is seen by some
as a necessary evil in the name of scientific advance while
others may think it is probably one the greatest sins mankind
can commit against other species. Without entering in a profound
ethical debate about the need of using other species for medical
research, this article explores the importance of using rodents
to study the positive and negative effects nanotechnology
can have on the health of both humans and animals. Nanotechnology
can have applications in various areas of human and veterinary
medicine as in, for example drug delivery, drug discovery
and development of diagnostics and medical devices. These
applications can bring us a new era of preventive medicine,
where the treatment of diseases could be initiated even before
the first symptoms occur. In this article the word “rodent”
specifically refers to the group of small mammals commonly
use in animal research, which includes the rats and mice.
Why rodents are important to the nanomedical research? The
use of this group of small mammals will certainly have profound
implications for curing both human and companion animal diseases.
Thanks to new advances in the study of animal genetics, we
know that the genome of rodents and humans are very similar.
Of the thirty thousands genes possessed by a mouse, ninety-nine
percent have obvious counterparts in the human genome. It
is this kind of similarity that makes rodents so important
for the study of the medical applications of nanotechnology.
Animal
research has played a vital role in virtually every major
medical advance of the last century for both human and animal
health. Practically every present day protocol for the prevention,
control, and cure of disease and the relief of pain is based
on knowledge attained through research with laboratory animals.
Thanks to the use of laboratory animals, modern medicine has
boosted the average life span of Americans by almost thirty
years. Animal research has also resulted in many remarkable
life saving and life-extending treatment for companion animals,
wildlife and endangered species. It is estimated that ninety
percent of the animals currently use for medical research
are rats and mice. Rats and mice make good research subjects
for those studying the medical applications of nanotechnology
for a variety of reasons. First, they are biologically similar
to humans. Second, they are susceptible to many of the same
health problems as humans; and third, they have short life
cycles so they can easily be studied throughout their life
span or across several generations. In addition, scientists
can easily control the environment around the animal, which
would be difficult to do with human subjects.
The
use of rodents by the nanotechnology and biotechnology industries
can be of great importance to assess the potential toxicological
effects of certain nanoparticles. In theory, nanoparticles
can be produce from nearly any chemical; however, most nanoparticles
to which human and companion animals might be exposed have
been made from transition metals, silicon, carbon, metal oxides
and nanocrystals. Due to their physical and chemical characteristics,
nanoparticles may not be easily biodegradable or may not be
able to be removed by the immune system. Inhaled nanoparticles
can accumulate in the nasal cavities, lungs and brains of
rats and scientists speculate this buildup could lead to inflammatory
lesions in the respiratory systems, brain damage or central
nervous system disorders. These kinds of studies can provide
clues about potential occupational hazards in companies dealing
with the production of nanomaterials. The use of rodents will
not only be crucial to design adequate safety tests and to
establish proper safeguards in the work place, but will also
make an important contribution to the development of a sustainable
and safe nanotechnology.
Besides
toxicology studies, rodents are also major contributors to
other medical applications of nanotechnology. The first implantable
medical device using a combination of microtechnology and
nanotechnology was tried on diabetic rats. This medical device
consists of a silicon box a tenth of a millimeter across,
which interior contains collagen tissue seeded with pancreatic
cells. The silicon box is porous with holes twenty nanometers
wide that can permit glucose molecules pass from the blood
stream to the interior of the device without any problem.
If the pancreatic cells inside the device detect too much
glucose in the blood stream, they start producing insulin.
The insulin molecule is small enough to pass through the pores
into the blood stream lowering the glucose levels. One advantage
of using a device with nanopores like the one described here
is that big molecules such antibodies will not be able to
reach the interior of the device so the possibility of an
immune rejection to the pancreatic cells inside the device
is minimal. In theory, a diabetic rat with the implanted device
can survive a couple of weeks or longer without the need for
insulin shots.
Natural
resistance to the use of antibiotics has always been a topic
of concern in both human and veterinary medicine. One of many
nanomaterials that promises to be an important weapon in our
constant war against pathogenic bacteria is the nanotubes.
The bactericidal effects of nanotubes are due to their ability
to puncture the cell membranes. Once a cell membrane is punctured,
many of cell’s internal components squirts out producing the
immediate death of the bacteria. To prove the efficacy of
nanotubes as bactericidal agents, researchers have been experimenting
with live mice infected with lethal doses of Staphylococcus
aureus. The experiments shows that those mice injected with
specific doses of nanotubes survive the infection while those
who do not received the injection of nanotubes eventually
died. In some cases, it just takes a couple of hours or less
to see the positive effects of the nanotube injection. In
theory, any bacteria could eventually develop resistance to
a bactericidal drug made of nanotubes. But with simply doing
minor modifications to the structure or composition of the
nanotubes, we would be able to compensate to any drug resistance
that a bacteria may exhibit.
One
of the potential applications of nanoparticles is in the field
of diagnostics, which have been widely demonstrated thanks
in several studies using mice. The groups of nanoparticles
that show applications that are more promising are the quantum
dots. In one study involving mice, researchers injected human
prostate cancer cells under the skin of the rodents to promote
the growth of solid prostate tumors. The scientists then conjugated
a group of quantum dots to a highly specific monoclonal antibody
targeted to a prostate specific membrane antigen on the surface
of the prostate tumor cells. When they injected the conjugated
quantum dots into the circulatory system of the mice, the
dots selectively accumulated at the site of the tumor through
binding to the antigen target. This technique once refined
may offer the potential to diagnose certain tumors faster
that conventional methods commonly use today in veterinary
and human hospitals.
Besides
helping with the accurate diagnosis of tumors, nanoparticles
can also be used in the treatment of neoplasia. Using mice
infected with cancer cells scientists have shown that gold
nanoparticles can help X-rays kill cancerous cells more effectively.
The mice were divided into three groups. One group was treated
with a salt solution containing gold nanoparticles and irradiated
with X-rays. A second group received only the radiation treatment
while the third group was only treated with the gold nanoparticles
solution. Scientists have found that the mice treated with
the combination of nanoparticles, followed by X-ray treatment
have a reduction on tumor size or in certain cases the tumor
was completely eradicated. In the group that only received
the X-ray treatment the tumors continued to grow. In the third
group, the only use of gold nanoparticles showed no therapeutic
effect. The results of the study also shown that the one-year
survival rate for the combined treatment was eighty-six percent,
compared with twenty percent for the X-ray therapy alone,
and zero for the group treated with the nanoparticles alone.
The success on the group treated with gold nanoparticles and
X-rays is due to the fact that gold, which strongly absorbs
X-rays, tends to selectively accumulates in tumor instead
than in normal tissues. This behavior of the gold nanoparticles
opens the way to new possibilities for cancer treatment.
These are only examples of the potential benefits of using
rodents in medical studies dealing with the use of nanotechnology.
With the advances in this field is expected an increase in
the amount of rodents to be use for testing of new drugs or
medical procedures. We cannot forget that besides the use
of these tiny creatures, there is other alternatives to animal
testing that may provide us with faster results at lower costs.
These include bacteria and cell cultures, chemical tests,
computer models, and advanced statistical methods. Utilization
of these methods and better analysis of test results can help
the nanotechnology and biotechnology industries to reduce
the number of rodents needed for many experiments. It would
be nice if researchers avoid the use of animals when it is
possible to do while continuing with the search for alternative
methods of testing the possible medical applications of nanotechnology.
However, the use of rodents is going to remain an essential
part of the nanomedical research because nothing can substitute
for the complex functions of the whole living animal. New
drugs and medical procedures that derivates from the nanotechnology
research must still evaluated in animals before they can be
used on human patients. For these reasons, next time you take
a look of that cute long tailed mice at you near pet shop
or while on the store looking for the best rodenticide that
can get rid quickly of those pesky critters in your basement,
just remember that thanks to them you may be able to live
a longer, healthy and productive life.
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