|Scientists Link Chromatin Changes with Alcohol
Changes to genetic material in the brain may help induce the anxiety
that is characteristic of alcohol withdrawal, according to a new
study conducted in rats and supported by the National Institute
on Alcohol Abuse and Alcoholism (NIAAA), part of the National Institutes
of Health (NIH). The finding points to possible therapies to prevent
withdrawal-related anxiety, a driving force behind alcohol use
among dependent individuals.
"The novel mechanism described in this study is an intriguing
contribution to efforts aimed at defining the complex molecular
processes that underlie alcohol abuse and dependence," said
NIAAA Deputy Director Kenneth Warren, Ph.D.
Previous studies have implicated a brain structure known as the
amygdala in anxiety and alcohol-drinking behaviors. Other studies
have shown that chemical modifications to chromatin, the complex
of DNA and proteins within every cell nucleus, can influence the
expression of genes and thus may affect disease processes. Such
modifications to DNA or its associated proteins that do not affect
the DNA sequence are collectively referred to as epigenetic changes.
One typical chromatin modification involves the addition or removal
of acetyl groups — common components of many molecules in
biology — to or from chromatin proteins called histones.
In the current study, scientists found evidence that the removal
of acetyl groups (deacetylation) from histones in amygdala chromatin
was associated with increased anxiety brought on by alcohol withdrawal.
A report of the study, led by Subhash C. Pandey, Ph.D., professor
and director of neuroscience alcoholism research in the Department
of Psychiatry at the University of Illinois at Chicago and Jesse
Brown VA Medical Center in Chicago, appears in the April 2, 2008
issue of the Journal of Neuroscience.
The researchers modeled long-term alcohol use by maintaining adult
rats on a liquid diet containing alcohol. They found that when
alcohol was withdrawn from the rats' diet, the animals exhibited
significantly higher anxiety-like behaviors than did rats that
had been fed a non-alcohol diet. One means of measuring anxiety
used by the researchers was an apparatus known as an elevated plus-maze,
which consists of two open arms and two closed arms connected to
a central platform. Anxiety is gauged as a function of the amount
of time a rat spends in the closed versus the open arms of the
maze during a five minute testing period — the greater an
animal's level of anxiety, the less open-arm activity it displays.
The activity of histone deacetylases (HDAC), enzymes that remove
acetyl groups from histone molecules was increased in the amygdala
of alcohol-fed animals during withdrawal, and was reflected in
a reduction in acetylation of histone proteins H3 and H4 in the
central and lateral areas of the amygdala. They also found that
alcohol withdrawal led to reduced levels of neuropeptide Y (NPY),
a molecule known to play a role in anxiety and alcohol-drinking
behaviors, in the amygdala of the alcohol-fed rats. By blocking
HDAC activity with an HDAC inhibitor known as trichostatin A, the
researchers prevented the development of alcohol withdrawal-related
anxiety, and restored levels of histone acetylation and NPY.
"This is the first direct evidence implicating the HDAC-induced
chromatin remodeling in the amygdala as a major factor in the molecular
processes of alcohol addiction and further suggests that HDAC inhibitors
may be potential therapeutic agents in treating alcoholism," said
"This study demonstrates that alcohol exposure can cause
epigenetic changes to chromatin, altering gene expression and behavior," added
Antonio Noronha, Ph.D., director of NIAAA's Division of Neuroscience
The researchers also investigated the potential role played by
chromatin modifications in the anxiety-reducing effect that occurs
with exposure to low levels of alcohol. Rats injected with a one-time
dose of alcohol exhibited less anxiety than control animals. And
in contrast to the increased HDAC activity observed during withdrawal-related
anxiety, HDAC activity was inhibited during one-time alcohol exposure,
while histone acetylation and NPY expression in the amygdala was
Dr. Pandey noted that another class of enzymes — histone
acetyltransferases (HATs) — also regulate the addition of
acetyl groups to histone molecules. He and his colleagues found
that levels of a protein known as CREB binding protein (CBP), which
contains HAT enzymatic activity, were increased by single-dose
alcohol exposure but were decreased during ethanol withdrawal in
alcohol dependent animals.
"Thus, both HDAC and HAT may be involved in the dynamic process
of chromatin remodeling in the amygdala during alcoholism," he
said. "Future studies will examine chromatin remodeling-linked
epigenetic mechanisms of changes in expression of genes in the
amygdala or other brain regions during alcohol tolerance and dependence."
The National Institute on Alcohol Abuse and Alcoholism, part of
the National Institutes of Health, is the primary U.S. agency for
conducting and supporting research on the causes, consequences,
prevention, and treatment of alcohol abuse, alcoholism, and alcohol
problems and disseminates research findings to general, professional,
and academic audiences. Additional alcohol research information
and publications are available at www.niaaa.nih.gov.
The National Institutes of Health (NIH) — The Nation's
Medical Research Agency — includes 27 Institutes and
Centers and is a component of the U.S. Department of Health and
Human Services. It is the primary federal agency for conducting
and supporting basic, clinical and translational medical research,
and it investigates the causes, treatments, and cures for both
common and rare diseases. For more information about NIH and
its programs, visit www.nih.gov.