Gulf War illness could be caused by a class of chemicals known as organophosphates, which can include popular pesticides and insecticides but also the nerve gases sarin and cyclosarin.
The Department of Defense and the Central Intelligence Agency estimate 100,000 people might have been exposed to low levels of those nerve gases when troops blew up a weapons depot in Khamisiyah, Iraq, on March 10, 1991. Troops were also routinely exposed to the chemical in insecticides, said Dr. Alvin Terry, the director of the Animal Behavior Center at GHSU and professor of pharmacology and toxicology.
Terry and a colleague, Dr. Nathan Yanasak, have an $860,000, three-year grant from the DOD to study whether the chemicals can cause nerve damage in the brains of animals – in this case, mice – that could lead to memory and attention problems. They will look to see whether the insecticide chlorpyrifos, which is commonly used on crops in the U.S. and around the world – when given in low doses – might hamper the ability of the nerve cells to transport food and waste up and down the nerve.
“For it to maintain its health, it has to be able to transport things” along the axon of the nerve, Terry said. The researchers are using newer technology, such as manganese-enhanced MRI, to study that because manganese is known to be taken up and transported by nerves in the brain, he said. Researchers will also check whether the protective sheath of the nerve cells, known as myelin, is depleted by the low-level exposure, which can affect nerve firing.
“It’s probably subtle if it is there,” Terry said.
In previous work, including a study published this year, Terry and colleagues showed that “subthreshold” doses of the chemical caused memory and attention problems in rats even months later.
“Long after they have been exposed, you can still pick up on these memory deficits,” he said.
What makes that intriguing is that it is similar to problems that plague veterans with Gulf War illness, Terry said. The study in animals is is being done to find out whether that is the cause of the symptoms, which could stem from a number of other causes, such as the oil well fires that raged during the conflict and had wide exposure, Terry said.
“There’s a whole multitude of things that you could say might be a possibility,” he said. The DOD has funded research over the years into what might cause Gulf War illness, “but no one has really solved it. There have been a lot of controversies.”
His work has drawn some fire from chemical companies, but Terry said he strives for balance in his view of the chemicals.
“They have without a doubt dramatically improved farming productivity, and they have helped to get rid of vector-bone illnesses,” he said. “It’s just knowing the long-term effects; we need to be more educated on that and try to be balanced.”
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MORE INFORMATION
Additional information about this study from the Gulf War Illness (GWIRP) Congressionally Directed Medical Research Program (CDMRP)
Organophosphate-Related Alterations in Myelin and Axonal
Transport in the Living Mammalian Brain
Principal
Investigator:
TERRY, ALVIN V
Institution
Receiving Award:
GEORGIA HEALTH SCIENCES UNIVERSITY
Program: GWIRP
Funding
Mechanism:
Investigator-Initiated Research Award
Partnering
Awards:
Award
Amount: $859,673.00
PUBLIC ABSTRACT
Among the
variety of chronic symptoms that have been reported in those who suffer from
Gulf War Illness (GWI), the neurological problems, especially the deficits in
attention, concentration, and memory function, may be the most debilitating.
Unfortunately, despite more than 20 years of research, the exact cause of these
symptoms remains unclear. It has been hypothesized that a significant
contributing factor to GWI symptoms may have been exposure to the class of
chemicals known as organophosphates. These chemicals are found in many of the
insecticides used in the campaign during the Gulf War, as well as nerve agents.
Two nerve agents within the class of organophosphates, sarin and cyclosarin,
may have been released into the environment at low levels following the
destruction of an Iraqi munitions storage complex at Khamisiyah, Iraq, in March
1991. However, it has been very difficult to determine if exposure to
organophosphates, specifically, underlie the cognitive deficits or the changes
in brain structure (white matter volumetric changes) that have been recently
detected in Gulf War Veterans by magnetic resonance imaging (MRI). The
uncertainty arises because of the wide variety of other possible contributing
factors (multiple vaccinations, treatments with drugs like pyridostigmine
bromide, exposure to smoke from oil well fires, infectious organisms, etc.).
Accordingly, one goal of the proposed studies is to determine in animals if
exposures to organophosphates at levels that do not cause acute symptoms of toxicity
(i.e., similar to the situation with Gulf War soldiers) indeed result in
changes in the brain that have been documented by MRI studies in Gulf War
Veterans. These types of prospective studies can only be conducted in animal
models. We have already published several studies in animals showing that such
exposures to organophosphates can result in prolonged deficits in cognitive
function.
In
addition, the diverse and chronic nature of the neurological symptoms of GWI
suggests that some basic or fundamental neuronal process was adversely affected
while these individuals were stationed in the Persian Gulf area. In previous
work we have shown that one such fundamental process, axonal transport, the
mechanism whereby important molecules are transported in nerve cells, is
impaired in peripheral nerves of animals previously exposed to
organophosphates. Our next objective is to determine if axonal transport is
impaired in the brains of living animals after exposure to organophosphates,
establishing a plausible explanation for the variety of neurological symptoms
observed in sufferers of GWI. We have developed the capabilities to investigate
each of these phenomena (white matter volumetric and structural changes as well
as axonal transport) in the brains of living animals using two magnetic
resonance imaging techniques, diffusion tensor imaging (DTI) and
manganese-enhanced magnetic resonance imaging (MEMRI). We will study the
effects of several doses of a representative organophosphate insecticide that
was used during the Gulf War, chlorpyrifos, and a representative nerve agent,
diisopropylfluorophosphate. It is expected that the results of these studies
will not only contribute to a better understanding of the basis for the
neurological symptoms of GWI (the first step before new therapeutic targets can
be identified and new treatments can be developed), but also a better
understanding of the long-term toxicity of a class of chemicals that continues
to pose a significant risk for military personnel as well as millions of
civilians worldwide.
TECHNICAL ABSTRACT
Background: It has been hypothesized that a
significant contributing factor to the cognitive dysfunction and other
neurological symptoms reported in those who suffer from Gulf War Illness (GWI)
may have been exposures to the class of chemicals known as organophosphates
(OPs). However, there are confounding factors that limit the strength of this
hypothesis (e.g., other environmental exposures, vaccinations, etc.). The
proposed studies will determine prospectively in living animals if OP exposure
is associated with pathological features (e.g., myelin-white matter anomalies)
that have been observed in Veterans suffering from GWI. The proposed studies
will also prospectively examine the effects of OPs on a process (axonal
transport) that is fundamental to the function of neurons (i.e., effects that
could theoretically explain the diverse neurological symptoms of GWI).
Objective/Hypothesis: The objective of this application
is to determine if exposure to OPs results in alterations in myelin (as
observed in GWI patients) and axonal transport (as we have observed ex vivo in
animals) in the living rodent brain. Our central hypothesis is that OPs
compromise the integrity of myelin and impair axonal transport, effects that
lead to functional impairment of neuronal pathways that support cognition and
other neurological processes. We propose to study two OPs, a representative
insecticide that was used in the first Gulf war, chlorpyrifos (CPF), and a
representative nerve agent, diisopropylfluorophosphate (DFP).
Specific Aims: (1) Determine the consequences of
repeated subthreshold exposures (defined as doses not associated with signs of
acute toxicity) to representative OPs on axonal transport in the living rat
brain. (2) Determine the consequences of repeated subthreshold exposures to
representative organophosphates on myelin in the living rat brain.
Study Design: For Aim 1 we will determine if
OP-related axonal transport deficits occur in vivo using manganese-enhanced
magnetic resonance imaging (MEMRI) of the optic nerve axonal projections from
the retina to the superior colliculus. To quantify Mn[2+] enhancement, manually
drawn regions of interest (ROI) will be placed in 2D slices in various selected
areas (eyeball, optic nerve, superior colliculus) along the Mn[2+]-enhanced and
contralateral non-enhanced areas. The enhancement ratio within the ROI will be
calculated by dividing the enhanced ROI intensity by the contralateral
unenhanced ROI intensity.
For Aim 2
we will use image-based segmentation of brain tissue as well as diffusion
tensor imaging (DTI) to characterize changes in rat white matter (WM) after OP
exposure. Segmentation of WM and grey matter (GM) and subsequent volumetric
quantification of total WM, GM, and ventricular volume will offer a measure of
gross tissue integrity. Fractional anisotropy (FA) and diffusivity along radial
and axial directions of major neural bundles will provide three metrics for
quantifying changes in myelin. These bundles and tracks will include the optic
nerve, corpus callosum, corticospinal tracts, and additional regions that are
known to be important for cognitive function (e.g., the fornix, and stria
terminalis). DTI-based metrics (which provide an indirect probe of myelin
alterations in vivo) will be interpreted in conjunction with Black Gold II
histology and microscopic analysis (with unbiased stereology) of tissues from
additional OP-treated animals. Quality assurance of DTI performance will be
ensured using phantom objects with anisotropic diffusive characteristics imaged
simultaneously during the rat imaging sessions.
We will
evaluate three doses of CPF (3.0, 10.0, 18.0 mg/kg) and DFP (0.125, 0.25, 0.50
mg/kg) + vehicle controls administered daily for 14 days. For MEMRI and DTI
studies, six animals from each dose group will have baseline scans, will be re-scanned
at the end of OP dosing, and then re-scanned again after a 4-week, OP-free
washout period. Six additional animals from each dose group will be sacrificed
for Black Gold histology at the end of dosing and an additional six animals
will be sacrificed 4 weeks after the last OP exposure.
Impact: The proposed studies have been
designed to address the question of whether exposure to OPs was likely to have
been a causal factor in the pathological abnormalities observed in sufferers of
GWI. It is expected that the results will not only contribute to a better
understanding of the basis for the neurological symptoms of GWI (the first step
before new therapeutic targets can be identified and new treatments can be
developed) but, also, a better understanding of the long-term toxicity of a
class of chemicals that continues to pose a significant risk for military
personnel as well as millions of civilians worldwide.
Study participants were randomly assigned treatment with acupuncture, standard treatments such as drugs and physical therapy, or “fake” acupuncture in which needles were inserted at points other than the traditional meridians.
