Alcohol ADME in Primates Studied with Positron
Zizhong Li1*, Youwen Xu1, Don Warner1, Nora D. Volkow2,3
1Medical Department, Brookhaven National Laboratory, Upton, New York, United States of America, 2National Institute on Alcohol Abuse and Alcoholism, Bethesda,
Maryland, United States of America, 3National Institute on Drug Abuse, Bethesda, Maryland, United States of America
Background and Purpose: The sensitivity to the intoxicating effects of alcohol as well as its adverse medical consequences
differ markedly among individuals, which reflects in part differences in alcohol’s absorption, distribution, metabolism, and
elimination (ADME) properties. The ADME of alcohol in the body and its relationship with alcohol’s brain bioavailability,
however, is not well understood.
Experimental Approach: The ADME of C-11 labeled alcohol, CH311CH2OH, 1 and C-11 and deuterium dual labeled alcohol,
CH311CD2OH, 2 in baboons was compared based on the principle that C–D bond is stronger than C–H bond, thus the
reaction is slower if C–D bond breaking occurs in a rate-determining metabolic step. The following ADME parameters in
peripheral organs and brain were derived from time activity curve (TAC) of positron emission tomography (PET) scans: peak
uptake (Cmax); peak uptake time (Tmax), half-life of peak uptake (T1/2), the area under the curve (AUC60min), and the residue
Key Results: For 1 the highest uptake occurred in the kidney whereas for 2 it occurred in the liver. A deuterium isotope
effect was observed in the kidneys in both animals studied and in the liver of one animal but not the other. The highest
uptake for 1 and 2 in the brain was in striatum and cerebellum but 2 had higher uptake than 1 in all brain regions most
evidently in thalamus and cingulate. Alcohol’s brain uptake was significantly higher when given intravenously than when
given orally and also when the animal was pretreated with a pharmacological dose of alcohol.
Conclusion and Implications: The study shows that alcohol metabolism in peripheral organs had a large effect on alcohol’s
brain bioavailability. This study sets the stage for clinical investigation on how genetics, gender and alcohol abuse affect
alcohol’s ADME and its relationship to intoxication and medical consequences.
Citation: Li Z, Xu Y, Warner D, Volkow ND (2012) Alcohol ADME in Primates Studied with Positron Emission Tomography. PLoS ONE 7(10): e46676. doi:10.1371/
Editor: Martin W. Brechbiel, National Institute of Health, United States of America
Received June 3, 2012; Accepted September 3, 2012; Published October 1, 2012
This is an open-access article, free of all copyright, and may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for
any lawful purpose. The work is made available under the Creative Commons CC0 public domain dedication.
Funding: ZL was supported by a grant from Brookhaven National Laboratory (LDRD#03-103)and he is the author of a grant from National Institute on
Alcoholism and Alcohol Abuse (5R21AA014018-03). This research was also funded by United States Department of Energy (DE-AC02-98CH1-886) and National
Institutes of Health (Intramural Research Program of the National Institute on Alcoholism and Alcohol Abuse). The funders had no role in study design, data
collection and analysis, decision to publish, or preparation of the manuscript.
Competing Interests: The authors have declared that no competing interests exist.
* E-mail: Zizhong_li@eisai.com
The evaluation of alcohol’s ADME in intact animals is
complicated by the fact that alcohol and its major metabolites:
acetaldehyde, acetate, and carbon dioxide, are small and rapidly
diffusible molecules that can penetrate cellular membranes and
diffuse within the water volume of the body. In addition, no high
affinity non-covalent ethanol binding sites have yet been found. As
a result, the binding and bio-distribution assays with radiolabeled
ligands that are routinely used in pharmacology research are not
suitable for studies of alcohol’s ADME.
Enzymatic oxidation of ethanol to acetaldehyde and then to
acetic acid is the major ethanol metabolic pathway in vivo. Clinical
studies suggest that organ damage from excessive alcohol
consumption is at least partially related to alcohol metabolic
products [1,2]. Slower acetaldehyde metabolism in Asian popu-
lations is responsible for their lower lifetime prevalence of alcohol
abuse disorders than in other ethnic groups [3,4], but it is also
responsible for the significantly higher risk of digestive tract
cancers among heavy drinkers [5,6,7]. Greater brain atrophy 
and liver and cardiac damage among women alcoholics than
among men might be attributed to gender differences in
metabolism of alcohol [9,10,11,12]. Similarly differences between
men and women in the sensitivity to alcohol’s behavioral and
central neurological effects are likely to reflect in part differences in
alcohol’s metabolism by peripheral tissues [8,13]. Metabolism of
alcohol in the brain may also modulate its behavioral effects as
shown in rats that the oxidation of alcohol to acetaldehyde by
catalases in the Ventral Tegmental Area (VTA) was reported to be
essential for alcohol’s rewarding effects .
Alcohol’s elimination in experimental animals has been studied
by monitoring blood ethanol concentration and the distribution of
stable isotopically and radioisotopically labeled ethanol and its
isotopologues [15,16,17]. Detailed physical and biochemical
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transformation data of ethanol in isolated liver , lung ,
kidney , and brain [21,22,23] have been reported. There are,
however, few studies on alcohol’s whole body regional distribution
and pharmacokinetics in intact primates. In cats, studies with
carbon-11 labeled alcohol showed high levels of radioactivity in
liver, heart and head, which presumably reflected the accumula-
tion of alcohol or its metabolic products in these organs .
In humans, the brain imaging studies with magnetic resonance
spectroscopy (MRS) showed that ethanol’s concentration in the
brain plateaus at around 35 min after oral administration of
pharmacological doses of ethanol . A brain imaging study with
positron emission tomography (PET) and O-15 water (marker of
blood flow) and C-11 ethanol suggested that ethanol’s distribution
in brain was in part mediated by interactions with GABA and/or
NMDA receptors . Glutamate, voltage-gated calcium chan-
nels, opioid, dopamine, serotonin, and acetylcholine receptors are
affected by alcohol, but the interaction of ethanol with these
receptors is believed to be transient and of low affinity apparently
acting as a ‘‘molecular lubricant’’ that alters the protein function
PET is a tool of choice to study drug distribution in human and
experimental animals in real time. The combination of PET and
deuterium kinetics isotope effect can be used to differentiate a
drug’s biochemical mechanism in the organs of interest . The
deuterium isotope effect is based on the principle that the C–D
bond is stronger than C–H bond, and the reaction will be slower if
a C–D bond breaking is involved in a metabolic rate-determining
step. The deuterium isotope effect has been used to determine the
contribution of various ethanol oxidative metabolic pathways both
in vitro and in vivo[29,30]. Here we aimed to use C-11 labeled
alcohol, 1 and C-11 and deuterium dual labeled alcohol, 2 as a
pair of PET tracers to study alcohol ADME in the baboon
including its metabolism within the various organs. We also
evaluated the relationship between overall alcohol’s ADME in the
various organs of the body and its bioavailability in the brain.
Thus we hypothesize that, in the same subject, we would observe a
significant isotope effect in the liver and the kidneys, which are the
organs that metabolize alcohol but not in heart and lungs, which
don’t metabolize alcohol. We do not expect to observe significant
isotope effect in the brain due to its negligible contribution to the
overall alcohol metabolism , however uptake pattern differ-
ence of 1 and 2 in different brain region in the same subject could
be indicative of isotope sensitive alcohol metabolism in brain.
The preparation of CH311CH2OH, 1 and CH311CD2OH, 2
Tracers 1 and 2 were prepared according to a modified
literature procedure . Briefly,11CO2from a target that was
trapped in a solution of methyl magnesium bromide (MeMgBr) in
ether. The product was then reduced by lithium aluminum
hydride or lithium aluminum deuteride, hydrolyzed by sodium
hydroxide aqueous solution (5 N) to give the crude 1 or 2
respectively with [11C]methanol (3 to 7%) and [2-11C]isopropanol
(5 to 30%) as the major radiochemical impurities. The reaction
mixture was then subjected to HPLC purification using a self-
packed fermentation column and water as elute and the purified
product was formulated into an injectable saline solution. The
radiochemical purity of C-11 ethanol was greater than 99%
without detectable chemical and radio-chemical impurities in the
Baboon studies were approved by the Institutional Animal Care
and Use Committee of Brookhaven National Laboratory and the
baboons were housed and maintained in an accredited animal
facility certified by the Association for Assessment of Laboratory
Animal Care. Animals had free access to food, water and toys and
were monitored during study by veterinary stuff. PET studies were
performed on four female baboons (Papio Anubis). Baboons were
anesthetized with an intramuscular injection of ketamine hydro-
chloride (10 mg/kg), intubated, and for studies in which alcohol is
administrated orally, a nasogastric tube was installed. The baboon
was transported from animal facility to the PET laboratory by a
certified veterinary nurse and maintained on a gaseous mixture of
oxygen, nitrous oxide, and isoflurane throughout the imaging
session. Catheters were placed in an antecubital vein for
radiotracer injection and for plasma sampling for radioactive
alcohol, acetaldehyde, and acetic acid quantification. EKG, blood
pressure, O2saturation, and respiratory setting were continuously
monitored throughout the study.
PET scans were performed on a Siemens HR+ high resolution,
whole-body PET scanner (63 slices, 4.564.564.8 mm) in 3-
dimensional acquisition mode. Before each scan, a transmission
scan was obtained with a68Ge rotating rod source for attenuation
correction. For brain imaging, the head of the baboon was
positioned at the center of the field as defined by imbedded laser
lines with help of a stereotactic head fixation device. The PET
measurements were carried out according to the protocols
described in Table 1. Data acquisition was started immediately
after the injection. The images were summed from 0 min to
59 min for liver, heart and lungs, and from 0 min to 10 min for
the brain. For the peripheral organs, circular regions of interests
(ROIs) were drawn manually on the heart, lungs, liver and the
kidneys on a summed image and projected onto dynamic images
to derive TAC. For the brain circular ROI were obtained in the
striatum, cerebellum, thalamus, occipital cortex, frontal cortex,
temporal cortex, cingulate, global (whole brain), and the white
matter. The average radioactivity in the ROIs from each organ
was taken as the tracer uptake in that organ. The images were also
reconstructed into dynamic images containing 27 continuous slices
to derive TAC. The area under the curve of each organ was
calculated by the trapezoidal method up to the termination of
acquisition (60 min). The baboon had a radial arterial cannula in
the wrist to permit continuous counting of blood radioactivity
concentration with a bismuth germinate counter during the course
of the experiment. Blood samples were also taken after the
injection and the activity in the blood sample was counted in a NaI
well counter to derive the plasma and the metabolites corrected
plasma curves. The radioactive ethanol, aldehyde, and acetic acid
were quantified with HPLC on a fermentation column. Acetate,
acetaldehyde, and ethanol eluted at 8, 10 and 12 min (elute:
30 mM HCl, flow rate 0.5 mL/min) respectively.
Peripheral organ uptake and the deuterium isotope
Alcohol ADME properties are affected by the genetic predis-
position, individual body composition, physical condition, and the
environmental factors including past history of alcohol use [33,34].
Individual variations in alcohol’s ADME in the liver, kidneys, lung
and heart were also observed between baboons. Therefore, we did
not attempt to average the PET data from different baboons for
Alcohol ADME in Primates Studied with PET
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peripheral ADME analysis; instead, we presented results from the
two baboons individually, April (BEJ129) and Missy (BEH131) in
whom we obtained measurements for the liver, kidneys, lung, and
the heart. The heart, lungs, liver, and the kidneys were easily
identified from the summed PET images of 1 and 2 (Fig 1). Tracer
1 had the highest uptake in the kidney, tracer 2, on the other
hand, had the highest uptake in the liver. The ADME of 1 and 2
were quantitatively assessed with the following parameters
(Table 2) derived from the TAC (Fig. 2a, 2b, 2c, 2d): peak uptake
(Cmax); the time at which peak uptake was observed (Tmax); time at
which peak uptake was reduced to half of its value (T1/2); area
under the curve (AUC60min) and residual uptake (C60min) at end of
the scan. Tracers 1 and 2 had different liver uptake patterns in
April and Missy (Fig. 2a): the radioactive C-11 from 1 had a lower
peak uptake (Cmax=0.048% ID . mL21) than that from 2
(Cmax=0.055% ID . mL21) in April (Table 2), whereas in Missy
peak uptakes from 1 (Cmax=0.036% ID . mL21) and 2
(Cmax=0.030% ID . mL21) were similar. Both tracers had slow
elimination rates (T1/2.50 min) from the liver. Tracer 1 had
lower liver exposure (AUC60min=1.92 min . % ID . mL21) than 2
(AUC60min=2.61 min . % ID . mL21) in April, whereas in Missy
liver exposures were similar (AUC60min=1.24 min . % ID . mL21
for 1 vs 1.11 min . % ID . mL21for 2) and the liver exposures
from both tracers were lower than that for April. Tracer 1 had a
lower residue uptake (C60min=0.026% ID . mL21) than 2
(C60min=0.038% ID . mL21) in April and a similar residue
uptake (C60min=0.018% ID . mL21for 1 and 0.016% ID . mL21
for 2) in Missy.
Tracers 1 and 2 had similar uptake patterns for April and Missy
in the kidney, heart, and the lung (Fig. 2b, 2c, 2d). A faster uptake-
elimination phase (Tmax=0.08 to 0.75 min; T1/2=0.3 to 1.8 min)
was followed by a slower uptake-elimination phase for 1 and 2 in
these organs for both baboons (Table 2). During the faster uptake-
elimination phase, the alcohol simply perfused through the organ
along with the blood flow with minimal biochemical tissue
interactions; we define this as the physical uptake-elimination
phase. In the slower uptake-elimination phase, alcohol and its
metabolites interact with tissues biochemically. Information from
the alcohol’s metabolism can be derived from the slower uptake
and elimination phase. Tracer 1 had higher uptake, faster
elimination, and higher residue uptake than 2 in the kidneys in
each baboon. The elimination of both tracers from the heart was
similar and in the lungs it was higher for 2 than 1 with T1/2from
20 to 32 min in lung and over 60 min in heart.
Alcohol brain uptake and deuterium isotope effect
To avoid intersubject variability, alcohol’s brain uptake were
studied in the same baboon (Pearl) with tracers 1and 2. The
metabolic effect on brain uptake was assess by observed deuterium
Table 1. Summary of Baboon PET studies.
Name of baboon
Administration method (dose and
formulation)The scan protocol
Brain uptake and deuterium isotope effect
BEJ135Pearl (14 kg)Brain1 (first scan) 2 (second scan)i.v. (75.48 MBq) (76.22 MBq)4630 s, 4660 s, 46120 s, 96300 s
BEJ142Pearl (14 kg)Brain1i.v. (164.28 MBq) 12610 s, 8630 s, 46120 s, 86300 s
BEJ152Pearl (14 kg)Brain 2 (first scan) 1 (second scan)i.v. (145.78 MBq) (145.78 MBq)12610 s, 8630 s, 46120 s, 86300 s
BEJ166Pearl (15.1 kg)Brain 2 (first scan) 1 (second scan)i.v. (42.55 MBq) (140.60 MBq) 12610 s, 8630 s, 46120 s, 86300 s
BEJ167Spicey(17.4 kg)Brain2 (first scan) 1 (second scan)i.v (142.82 MBq) (109.52 MBq) 12610 s, 8630 s, 46120 s, 86300 s
BEJ179 Pearl(N/A)Brain 1 (first scan) 1 (second scan)i.v (139.12 MBq) (165.02 MBq) 12610 s, 8630 s, 46120 s, 86300 s
Peripheral uptake and deuterium isotope effect
BEH131Missy(15.5 kg)Torso 2 (first scan) 1 (second scan)i.v (175.01 MBq) (101.01 MBq) 12610 s, 8630 s, 46120 s, 146300 s
BEH189 April (N/A)Torso 2 (first scan) 1 (second scan)i.v. (85.47 MBq) (85.47 MBq)4630 s, 4660 s, 46120 s, 96300 s
BEJ129April (13.4 kg)Torso1 (first run) 2 (second run) i.v. (106.93 MBq) (111.27 MBq)4630 s, 4660 s, 46120 s, 96300 s
BEH137 Pearl (N/A)Torso 2 (first scan) 1 (second scan) i.v. (122.10 MBq) (127.28 MBq)4630 s, 4660 s, 46120 s, 96300 s
BEJ158Pearl (14 kg)Brain1Oral (341.51 MBq of 1 in 10 mL ethanol
and 35 mL water)
5660 s, 56180 s, 56240 s, 66300 s,
BEJ196 Missy (N/A)Brain 1 (first scan) i.v. (166.13 MBq, 35 min after pretreat
with 45 ml water)
12610 s, 8630 s, 46120 s, 146300 s
1 (second scan)i.v. (185.37 MBq, 35 min after pretreat
with 10 ml ethanol and 35 ml of water)
1: CH311CH2OH; 2: CH311CD2OH
Figure 1. Summed images of tracer 1 (A, top) and tracer 2 (B,
bottom) in lung, heart, liver and kidney (from 0 to 60 min) in
baboon (April). Tracer 1 had the highest uptake in kidney; tracer 2,
had the highest uptake in liver.
Alcohol ADME in Primates Studied with PET
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isotope effect. A total of nine studies were conducted, six with 1
and three with 2. Alcohol was distributed in most of the brain
(Cmax=0.028% ID . mL21) and cerebellum (Cmax=0.026% ID
. mL21) for 1 and in striatum (Cmax=0.034% ID . mL21),
cingulate (Cmax=0.033% ID . mL21), cerebellum (Cmax=0.031%
ID . mL21), and thalamus (Cmax=0.030% ID . mL21) for 2 (Fig 3).
The Cmaxratio of brain to blood obtained during the first 3
minutes is 0.13 for 1 and 0.18 for 2. Tracer 2 had consistently
higher peak uptake (Cmax) than 1 in all brain regions studied
(Fig 4). The Cmaxratio for the peak uptake of 2 to 1 was highest in
Cmax(1)=1.10) (Fig S1).
Figure 2. Time activity curves in liver (TAC) (a); kidney (b); lung (c); heart (d) in baboons (April: BEJ129 and Missy: BEH131) and
Brain (e) and blood (f) in baboon (Pearl: BEJ152a) of tracers 1 (H) and 2 (D).
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Table 2. Pharmacokinetics assessment of alcohol after iv administration to baboon.
Organ Study tracerCmax(% ID . mL21)Tmax(min)T1/2(min)
AUC60min min . % ID .
C60min % ID . mL21
liver BEJ12910.048 0.055 0.036 0.030 3.00 7.00 1.25 1.25
.60 .60 52.0 52.0 1.920.0260
fasterslower fasterSlower Fasterslower
kidney BEJ12910.0940.1100.753.00 ND11.01.620.0164
2 0.0610.060 0.75 3.00ND14.01.05 0.0146
BEH13110.122 0.128 0.422.50 ND11.0 2.35 0.0134
2 0.0840.0830.42 2.75 ND 14.01.81 0.0109
lung BEJ1291 0.0490.0180.25
brainBEJ1521 0.015 0.0200.60 0.604.00 4.000.23 0.0029
blood BEJ1521 0.118 0.118 0.42 0.420.75 0.750.21 0.0040
brainBEJ1961Brain uptake plateaued at ca. 15 min0.12 0.0027
Cmax, peak uptake; Tmax, time at which peak uptake was observed; T1/2, time at which uptake reduced to half of its peak value; AUC60min: area under time activity curve
from 0 to 60 min; C60min residue uptake at end of scan
Figure 3. Summed images of tracers 1 (A) and 2 (B) in the brain
of Pearl (from 0 to 10 min), alcohol distributed in all brain
regions. Tracer 1 showed higher uptake in striatum and cerebellum;
and tracer 2 in striatum, thalamus, cerebellum, and cingulate. Tracer 2
had consistently higher uptake than 1 across all brain regions.
Figure 4. Brain uptake (Cmax) of tracers 1 (H) and 2 (D) in
baboon (Pear) in different brain region. STR: Striatum; CB:
Cerebellum; THL: Thalamus; OCC: Occipital cortex; FRT: Frontal cortex;
TEMP: Temporal cortex; CING: Cingulate gyrus; GL: Global; WM: White
matter. Tracer 2 shows consistent higher uptake than 1 in all brain
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To further study the effect of metabolism on alcohol’s brain
uptake we conducted a pair of sequential studies in the same
baboon (Missy) with 1 (BEJ196): the first scan after pretreatment
with water (45 ml), and the second one, 35 minutes after
pretreatment with a pharmacological relevant dose (5.6 g/kg) of
alcohol (22% alcohol by volume (ABV), 45 mL). Pretreatment
with alcohol significantly increased the brain uptake of alcohol in
all brain regions (Fig 5). To evaluate the effect of the first pass
metabolism and intestine permeability on alcohol brain uptake, a
(341.51 MBq) was administered to Pearl (BEJ158) orally, the
brain alcohol uptake plateaued at approximately 15 min in all
brain regions and remained at that level throughout the 60
minutes of the study (Fig 6). The study BEJ158 (oral 1 in a
pharmacological dose of alcohol) was compared with the BEJ196
second scan (intravenous 1 after an oral pharmacological dose of
alcohol) (Fig 6), and 1 was found to have a much higher brain
exposure and peak uptake after iv than after oral administration.
However at 50 minutes the brain concentration of alcohol was
similar for iv and oral administration.
Discussion and Conclusions
Ethanol is metabolized to acetaldehyde in the body through
three major pathways: (1) an alcohol dehydrogenase (ADH)
pathway, which accounts for over 85% of ethanol’s oxidation and
has a deuterium isotope effect of 3 and is pH (pH=7) and
coenzyme dependent (coenzyme NAD+) , ADH pathway is
reversible in vivo and a reversible-ADH pathway converts
acetaldehyde back to alcohol and causes the hydrogen for
CH3CDHOH to CH3CH2OH) eliminating the deuterium isotope
effect ; (2) catalase pathway, which eliminates about 2%
ethanol and has a deuterium isotope effect of 1.9 determined from
rat and ox liver catalase [36,37]; and (3) the microsomal ethanol-
oxidizing system (MEOS) is a minor metabolic pathway in healthy
humans, but in alcoholics it can account for up to 10%  of
ethanol’s elimination in the liver and has a deuterium isotope
effect from 3.6 to 5.2 . Acetaldehyde is then oxidized to
acetate by acetaldehyde dehydrogenase (ALDH) and it has a
deuterium isotope effect of 2.8 .
The liver is by far the most important organ for ethanol’s
elimination and it contains almost all the ethanol metabolic
enzymes. In healthy animals or humans, hepatic alcohol
metabolism is responsible for over 95% of ethanol’s oxidation.
Individual genetic makeup and environmental condition could
alter the contribution of individual metabolism pathways to the
overall alcohol metabolism . The two baboons in whom we
studied, the liver differed in their metabolism of 1 and 2 as
evidenced by their liver TAC profiles (Fig 2a), which represent
hepatic uptake and elimination kinetics for all C-11 labeled species
derived from C-11 labeled alcohol including C-11 labeled alcohol,
acetaldehyde, acetate, carbon dioxide, and higher molecular
metabolites. The hepatic TAC profiles for 1 and 2 were different
in April (higher for 2 than 1), but similar in Missy. The liver TAC
patterns for 1 and 2 could be used as a biomarker to assess the
contributions from different alcohol metabolism pathways to
overall hepatic alcohol metabolism, the reliability of such marker
would have to be confirmed by enzyme inhibition and in a larger
Studies done in ex-vivo isolated renal tissue (cortex and tubules)
from baboons showed that the reversible ADH pathway is present
in the kidney. In the kidney, acetaldehyde can be metabolized at a
high rate and in a dose dependent manner and converted to
ethanol, acetate and carbon dioxide; at acetaldehyde concentra-
tion from 1 mM to 20 mM the major product is acetate and at
higher acetaldehyde concentration the major product is ethanol
[20,42]. Our PET images show that in the kidneys ethanol’s
metabolism mainly took place in the cortex (Fig 1). The activity
derived from 1 was eliminated consistently faster (T1/2=11 min)
than 2 (T1/2=14 min) in both baboons (Table 2), this isotope
effect may indicate the contribution of oxidation of acetaldehyde
(CH3CHO from 1 or CH3CDO from 2) to acetate. The slower
elimination of 2 than 1 in both baboons may suggest the
transformation of acetaldehyde into acetate in the kidneys, which
Figure 5. Brain uptake (Cmax) of tracer 1 in baboon (Missy) in
different brain region. STR: Striatum; CB: Cerebellum; THL: Thalamus;
OCC: Occipital cortex; FRT: Frontal cortex; TEMP: Temporal cortex; CING:
Cingulate gyrus; GL: Global; WM: White matter. When baboon was
pretreated with water (45 ml) or alcohol (22% ABV, 45 ml).
Figure 6. Time activity curves for the global brain uptake when
tracer 1 was administered iv 35 min after baboon was
pretreated with alcohol (22% ABV, 45 ml), and when tracer 1
was administered orally with alcohol (22% ABV, 45 ml). The
brain exposure (AUC60min) was much higher when tracer 1 was
administered iv. GL: Global
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is supported by the well-recognized role that kidneys have in the
detoxification of alcohol from the body .
Studies on lung slices from rats and dogs showed that alcohol
dehydrogenase in pulmonary tissue can metabolize ethanol in a
bicarbonate buffer by sulfoconjugation [19,43] but in human this
is likely to be limited by the substrate availability. In the slower
uptake elimination phase, the time-activity-curve reached a steady
state in the lungs, which could be attributed to11CO2elimination.
The expiration of11CO2from ethanol showed that it reached a
steady state shortly after intravenous injection . The overall
slower metabolism of 2 would therefore result in a lower blood
concentration of11CO2, and less carbon-11 exchange in the lungs
residual activity (C60min) for 2 than for 1 (Table 2).
Like the lungs, the heart is not directly involved in oxidative
metabolism of ethanol. The overall heart exposure (AUC60min)
and heart residue uptake (C60min) for tracers 1 and 2 was similar
for both baboons (Table 2). Ethanol in the heart can be converted
into fatty acid ethyl ester (FAEE) by FAEE synthase enzyme,
which is detrimental to heart muscles . No carbon-hydrogen
bond is broken or made in this process, thus the deuterium isotope
effect is not expected.
Metabolism of ethanol in the peripheral organs has a significant
impact on the uptake of alcohol by the brain. The up-to-date
consensus has been that the acetaldehyde that is peripherally
derived does not penetrate the blood brain barrier in any
significant amount . The uptake of acetate by the brain is low
 but it increases during alcohol intoxication (Volkow et al
unpublished). Thus the radioactivity in the brain for both tracers
most likely reflected ethanol’s brain uptake with some contribution
from acetate particularly when given concomitantly with phar-
macological doses of alcohol. The slower metabolism of 2 resulted
in a higher plasma alcohol concentration, which would account for
its higher brain peak uptake (Fig 4). When the baboon was
pretreated with a pharmacological dose of alcohol, the alcohol
metabolizing enzymes (ie ADH and catalase) may have been
saturated resulting in the elevated tracer (1) blood concentrations
and higher brain uptake of 1 than when pretreated with water.
However, the higher blood flow  and the higher acetate
concentration in plasma under the influence of alcohol (Volkow et
al unpublished) may have also contributed to the initial higher
brain uptake of 1. This added to our findings of much lower brain
uptake after oral alcohol administration, which exposes alcohol to
the first pass hepatic metabolism, than after intravenous admin-
istration, and the higher brain uptake for 2, which has lower
peripheral metabolism than 1, provides further evidence that
peripheral metabolism of alcohol influences the uptake of alcohol
in the brain. To the extent that there are significant differences in
the rate of alcohol metabolism between individuals, including
greater metabolism in alcoholics than controls and greater
metabolism in males than females . This would contribute to
the differences in the sensitivity to alcohol’s psychoactive effects.
Alcohol distributed throughout the brain but there was a greater
uptake and accumulation in the cerebellum and striatum for both
tracers but also higher uptake in cingulate and thalamus for 2
(Fig 3). This is consistent with prior studies in the rodent brain that
showed the highest alcohol concentration in the striatum  and
with a prior PET study in cymologous monkeys that reported
higher [C-11]ethanol uptake in subcortical brain regions . The
higher uptake in striatum would underlie its rewarding effects,
which are mediated in part by its effects in ventral striatum
[51,52]. On the other hand the high accumulation of alcohol or its
metabolites in the cerebellum is consistent with findings that the
cerebellum is particularly sensitive to the decreases in brain
11CO2expiration, which would account for the lower
glucose metabolism after acute alcohol administration  and
could underlie the motor incoordination observed during intox-
The peak uptake (Cmax) ratio of brain to blood is 0.13 for 1 and
0.18 for 2, which occurs within the first 3 minutes after its
administration most likely reflects the high concentration of
alcohol in blood (Fig S2). However after 3 minutes the blood to
brain ratio reaches 1 and then slowly decreases, which is consistent
with our findings from MRS in humans showing blood to brain
ratios for alcohol around 1 or lower . Pharmacokinetic studies
of alcohol in the rat brain after an intraperitoneal injection showed
that its uptake in the first 5–10 minutes reflects primarily
absorption after which it reflects a combination of absorption,
metabolism, elimination and water/fat equilibration . Our
findings of a Cmaxratio of brain to blood obtained during the first
3 minutes of 0.13 for 1 and 0.18 for 2 and its rapid equilibration to
brain to blood ratios of 1 are also consistent with its uptake initially
being driven by its absorption and subsequently driven by a
combination of absorption, metabolism and clearance.
The first pass alcohol metabolism has a significant impact on the
alcohol blood concentration . Our PET data shows that the
area under the curve (AUC60min) after intravenous administration
is significantly higher than that after oral administration (Table 2,
BEJ158 and BEJ196) (Fig 6) indicating that gastric absorption and
the first pass alcohol metabolism significantly reduces alcohol
overall brain’s exposure and delays its arrival to the brain.
Limitation from our studies includes the fact that PET measures
the overall concentration of C-11 activity within the tissue but
cannot distinguish between alcohol and its metabolites. Also
because of the complexity and high cost of the studies, only a small
group of animals were used in the measurments that precludes us
from addressing the intersubject variability of alcohol’s ADME in
In conclusion, our studies demonstrate the value of using the
deuterium isotope effect and PET to investigate the ethanol
ADME properties in the liver, kidney, lung, heart, and the brain.
This study corroborates alcohol metabolism by the liver and
kidneys, and demonstrated that peripheral alcohol metabolism has
significant impact on alcohol’s brain bioavailability. These findings
sets the stage for future studies of alcohol in humans to investigate
how genetics, gender and alcohol abuse affect alcohol’s ADME in
the various organs, including brain and its relationship to
intoxication and medical consequences.
(H) in baboon (Pear) in different brain region. STR:
Striatum; CB: Cerebellum; THL: Thalamus; OCC: Occipital
cortex; FRT: Frontal cortex; TEMP: Temporal cortex; CING:
Cingulate gyrus; GL: Global; WM: White matter. The ratio was
highest in thalamus and cingulate gyrus and lowest in frontal
Brain uptake ratio (Cmax) of tracer 2 (D) to 1
(C(blood)) to tracer brain concentration (C(brain)) vs
time in baboon (Pear).
The ratio of tracer (1) blood concentration
We are grateful to Pauline Carter for animal handling, Payton King for
plasma analysis, David Schlyer and Michael Schueller for cyclotron
operation. ZL is indebted to Joanna Fowler for her mentorship and
teaching on research concept development, grant proposal writing, and
Alcohol ADME in Primates Studied with PET
PLOS ONE | www.plosone.org7 October 2012 | Volume 7 | Issue 10 | e46676
PET data analysis. This manuscript has been authored by Brookhaven
Science Associates. The United States Government retains, and the
publishers, by accepting the article for publication, acknowledge, a world-
wide license to publish or reproduce the published form of this manuscript
or allow others to do so, for the United States Government purposes.
Conceived and designed the experiments: ZL. Performed the experiments:
ZL YX DW. Analyzed the data: ZL NV YX. Wrote the paper: ZL NV
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