Download Neuropeptides and Anxiety: Focus on

CLIN. CHEM.
40/2, 315-318
(1994)
Neuropeptides and Anxiety: Focus on Cholecystokinin
R. Bruce
Lydiard
Cholecystokinin (CCK), a gastrin-like neuropeptide, exists
in the central nervous system in several forms. The octapeptide (CCK-8) occurs in predominantly sulfated form
(CCK-8S), and the tetrapeptide (CCK-4) occurs in smaller
but significant quantities. This review highlights recent
developments in preclinical and clinical research into the
potential role for CCK in mediating anxiety states. Relevant animal and human studies of administration of CCK
agonists are discussed,
as well as recent data regarding
the concentration of CCK-8S in cerebrospinal fluid from
patients with panic disorder, bulimia nervosa, and obsessive compulsive disorder. Finally, the development of
agents that specifically antagonize CCK receptors will be
described, as will potential therapeutic uses for these new
compounds.
IndexingTerms: mood disorders/bulimia neivosa/neurotransmitters/ panic disorder/cerebrospinal fluid
Increasing
predlinical
and clinical
evidence
implicates cholecystokinin
(CCK), a gastrin-like
material
found in the mammalian
intestinal
tract and central
nervous system (CNS), as a modulator
of neuronal functioning.’
CCK was first reported to occur in mammalian
brain in 1975 (1). CCK occurs in the CNS predominantly in two forms: CCK tetrapeptide
(CCK-4) and
CCK octapeptide
(CCK-8). These neuropeptides
appear
to act as neurotransmitters
themselves and to modulate
the activities of several other neurotransmitters
and
various
neuropeptides.
The predominant
form of CCK in
the CNS is the sulfated form of the octapeptide
(CCK8S), while CCK-4 exists in smaller
concentrations.
There are two predominant
receptor subtypes for CCK:
the CCK-A receptor (for “alimentary”)
and the CCK-B
receptor (for “brain”) (2). CCK-A receptors have a high
affinity for CCK-SS and lesser affinity for desulfated
CCK-8, CCK-4, and gastrin. The CCK-A receptors predominate in the periphery,
and occur in high concentrations in the viscera as well as in the CNS (3). The
CCK-B receptors, which have a high affinity for all CCK
agonists,
are the predominant
form in the brain. The
type A receptor in the CNS mediates
satiety and other
functions,
while the B receptor appears to be important
in mediating
anxiety.
The first description
of the anxiogenic
effects of CCK
were reported in a study of the mechanism
for satiety in
sheep (4). In this study, pentagastrin
was infused into
Institute of Psychiatry,
Medical University of South Carolina,
171 Ashley Ave., Charleston, SC 29425. Fax 803-792-9413.
‘Nonstandard
abbreviations: CCK, cholecystokinin;
CNS, central nervous system; GABA, y-aininobutyric
acid; 5-HT, serotonin;
NTS, nucleus tractus solitarius; and CSF, cerebrospinal fluid.
Received August 9, 1993; accepted October 5,1993.
the lateral ventricles of sheep and unexpectedly
elicited
behaviors consistent with anxiety,
such as foot stamping and vocalization.
Subsequent
studies in vitro and in
vivo have supported
the hypothesis
that CCK is an
important
neuropeptide
in the mediation
of anxiety in
animals
and in humans. This review will survey relevant preclinical
and clinical studies supporting a role for
CCK in anxiety,
and will also review the development
of
a new class of CCK-antagonist
compounds
with potential clinical utility.
Preclinical Studies
Early work by Bradwejn and de Montigny (5,6) showed
that benzodiazepines
specifically antagonized
CCK-8S-induced excitation
of rat hippocampal
pyramidal
neurons
but did not block the actions of other neurotransmitters
such as acetyicholine,
aspartate,
or glutamate.
Additionally, they showed that the antagonism
of the CCK-8Sinduced excitation
was specific for benzodiazepines,
as
demonstrated
by a lack of effect of haloperidol,
phenobarbital, and meprobamate
on this paradigm (6). These were
the first experiments
showing antagonism
of a central
action of a neuropeptide
by a benzodiazepine.
Behavioral
experiments
also supported a role for CCK in mediating
anxiety. Injection of CCK-8 into the amygdala enhanced
behavioral
arousal and fear-related
motivation
behaviors
in rats at very low doses (7). A substantial
literature
on
the anxiogenic
potential
of CCK agonists has emerged
over the past several years, and supports the role of the
CCK-B receptor in mediating
these effects (8). Recently,
CCK agonists have been studied in nonhuman
primates.
Ervin et al. described the effects of intravenous
administration of CCK-4 to African green monkeys (9). The behaviors elicited were consistent
with fear/panic-like
responses, including vigilance, agitation,
restlessness,
and,
at peak levels of intensity of the reactions, immobility or
freezing, which could be analogous to the human equivalent of panic. The response of the individual monkeys was
related to social hierarchy and to baseline behavioral characteristics of the individual
animals. Pretreatment
with
alprazolam or a specific CCK-B receptor antagonist
attenuated the effects of the CCK-4 challenge (10).
Additional
support for a potential role for CCK in
mediation
of anxiety states is the demonstrated
interaction of this peptide with neurotranamitters
implicated
in anxiety states, such as y-aniinobutyric
acid (GABA),
serotonin,
and norepinephrine.
Interaction
with the
GABA receptor complex, initially
demonstrated
in the
experiments
described above in which benzodiazepines
effectively and selectively blocked CCK-8S-induced
hippocampal
neuronal
excitation
(5, 6), is further
supported by the observation
that CCK and GABA are
colocalized in CNS neurons in cortex, hippocampus,
and
CLINICALCHEMISTRY,Vol.40, No. 2, 1994 315
amygdala
(8, 11). Further,
there appears to be a functional interaction
between
benzodiazepine
treatment
and the density of CCK receptors in certain brain areas;
this interaction
may have potential
links to tolerance
withdrawal
and to the anxiolytic
effects of the benzodiazepines (12). Serotonin
(5-HT), which has been implicated in anxiety, interacts with CCK Administration
of
ondansetron,
a specific 5-HT3-receptor
antagonist
with
anxiolytic
properties,
inhibits
the release of CCK-like
immunoreactivity
from limbic areas in rodents
(13).
Evidence indicating
an interaction
between norepinephrine and CCK includes the upregulation
of CCK receptors in hippocanipus
and frontal cortex alter chemical
lesion of the locus ceruleus,
a midbrain
noradrenergic
nucleus believed to mediate fear and arousal states (14).
Clinical Studies: Role of CCK in Stress and Panic Anxiety
CCK appears
to play a role in stress responses
in
humans.
In one recent study of marathon runners
(15),
19 athletes (8 women, 11 men) who were about to participate in a 46.5-km run were assessed for stress-relat.ed compounds
(cortisol, corticotropin,
CCK, norepinephrine,
and gastrin)
before and after the race, as well
as during a control condition. As expected, most of the
stress-related
compounds
were increased
before the
race, with CCK being the most increased.
The authors
hypothesized
that CCK was related to anticipatory
anxiety in these individuals
(15).
CCK-4 has been studied as a panic-inducing
agent in
humans. To expand on the predlinical
data as well as the
clinical observation that CCK-4 can induce panic-like
symptoms
in healthy volunteers
(16), Bradwejn et al.
embarked
on a series of experiments
to characterize
the
panicogenic
effects of CCK-4 in humans
(17). Initial
studies indicated
that patients with panic disorder experienced
panic attacks
after intravenous
administration of 50 g of CCK-4 but not after receiving a placebo
(18). Subsequent
studies indicated enhanced
sensitivity
to CCK-4 in panic disorder
patients vs normal volunteers (19). The symptom
profile-e.g.,
palpitations,
shortness of breath,
dizziness,
dyspnea,
and cognitive
symptoms
such as fear of losing control of one’s mind or
body or of dying-elicited
by CCK-4 in panic disorder
patients
appears to be similar to the effects of carbon
dioxide, another panicogenic
agent; both agents elicit
panic attacks that are described by patients with panic
disorder as being symptomatically
similar to those experienced
unexpectedly
(20). Bradwejn et al. also demonstrated that the CCK-4-induced attacks could be effectively
prevented
by pretreatment
with a CCK-B
antagonist
(21). Interestingly,
another CCK-like peptide, pentagastrin,
which differs by only one amino acid
from CCK-4, appears to be panicogemc
in individuals
with panic disorder (22) and elicits symptoms
similar to
those elicited by CCK-4 (23).
Although enhanced sensitivity to CCK-4 in panic disorder patients has been demonstrated,
the mechanism
by
which the CCK-4 exerts its panicogenic
effects remains
incompletely
understood,
there being no direct evidence
that CCK-4 crosses the blood-brain
barrier after intrave-
316 CUNICALCHEMISTRY,Vol. 40, No.2, 1994
nous administration.
It has been hypothesized
that the
effects of this peptide may be exerted on areas of the brain
where the blood-brain
barrier is incomplete, such as the
nucleus tractus solitarius (NTS) (8). This nucleus plays an
important role in mediating afferent input from periphery
and in acting as a relay for efferent signals that control
vegetative
functions,
and may mediate autonomic discharge such as occurs during unexpected
(and possibly
CCK-induced)
panic attacks
(24). For example, most NTh
neurons exhibit prolonged excitation after administration
of CCK-B agonists, whereas CCK-A agonists, which presumably interact with CCK-A receptors present in the
NTS, exert inhibitory
effects on NTS neurons and also
elicit brief, but not prolonged, excitation (8, 25). These
observations
suest
that the NTS may potentially
mediate at least in part some of the panicogemc
effects of
CCK-B agonists in humans.
Human Cerebrospinal Fluid (CSF) Studies of CCK
On the basis of the accumulating
evidence
of abnormal CCK function in panic disorder, my colleagues and
I examined CSF concentrations
of CCK-8S in panic disorder patients and in normal comparison
subjects (26).
We measured
CCK-85 because methods for measuring
CCK-4 in CSF are not sensitive
enough, but the octapeptide is present in quantities sufficiently large (i.e.,
ngfL) to be measured.
As can be seen in Fig. 1, CSF
concentrations
of CCK-8S in panic disorder patients
were lower than in normal comparison
subjects. The
finding of lower CSF concentrations
of CCK-8S in panic
disorder was thought to possibly reflect a reciprocal
relationship
between CCK-8 and CCK-4 in the CNS (27),
and might be a reflection of increased
CCK-4 activity,
with a resulting reciprocal
decrease
in CCK-8 activity.
40
30
U-
(1)
C.)
-a
--I--
-#{247}-
S
--:--
PD patients
(n=25)
Controls
(n=16)
Fig. 1. CSF cholecystokininconcentrationsin patients with
disorder(PD) vs normal subjects.
panic
Alternatively,
there may be increased receptor sensitivity or lower CCK-8 production,
as reflected by the lower
CCK-8S concentrations
in CSF in the panic patients.
We also measured
CSF concentrations
of CCK-8S in a
small number
of patients with obsessive compulsive
disorder, another
clinically
significant
anxiety
disorder
(28). In this small number
(n = 11) of patients, CSF
concentrations
of CCK-8S were not different from those
35
.o
30
0
,
‘
:
20
o
15
0
10
-
o
-.-
.
#{149}..
‘S
.
#{149}O
#{149}
5
0
in the normal comparison
subjects, suggesting
that alterations in CCK function, as reflected by CCK-8S concentrations,
may not be present in all anxiety disorders.
We subsequently
measured
CCK-8S concentrations
in
patients with bulimia nervosa, a condition characterized
by uncontrolled
eating binges and purging behaviors (Fig.
2). The CCK-8S concentrations
in CSF in patients with
biilimist nervosa were also lower than those of the normal
comparison
subjects (29). Because bulunuia nervosa could
be characterized, in part, as one of dysregulated
satiety,
the finding seemed to be consistent with the theory that
the central CCK function in bulimia nervosa was abnormal, paralleling
studies indicating
that the peripheral
CCK-8 function was abnormal
(30). Interestingly,
the
CCK-8 concentrations
in the subjects in this CSF study
did not correlate with any of the core symptoms
of the
eating disorder (e.g., binge frequency or intensity, purging), but did correlate with measures of anxiety, interpersonal sensitivity, and anger/hostility.
This raised the possibifity that the CSF abnormalities
of CCK-8S observed in
bulimicsmightbeassociatedmorewithabnormallevelsof
anxiety
than with core symptoms of eating disorder in this
patient sample.
CCK ReceptorAntagonists
BULIMIC
PATIENTS
NORMAL
COMPARISON
SUBJECTS
Fig. 2. CSF cholecystokinin concentrations in patientswith bulimia
nervosa vs normal subjects: 0, men; #{149},
women.
In recent years, specific and highly potent antagonists
for CCK receptors have been discovered and developed
(31). One of the first antagonists
discovered was apserlicm, a natUrally occurring benzodiazepune derived from a
fungus. Subsequently,
both benzodiazepine
and non-ben-
DEVAZEPIDE
(MK- 329, L-364, 718)
I
L-365, 260
I
I
....cHtcHtcHrcHrcH,
oc_a4cHccH_cH..cH..cHrcH
N-H
C-N*--M.O44H-COl1OO4j.H
LORGLUMIDE
(CR1409)
CCK-A Antagonists
Fig. 3. Structures
2
Cl-988
(PDI 34308)
CC*B
Antagonists
of some cholecystokininreceptorantagonists.
CLINICAL
CHEMISTRY,
Vol. 40, No. 2, 1994
317
zodiazepine-like
agents have been developed that are selective for either the CCK-A or CCK-B receptor (Fig. 3).
As a group, these compounds may represent a novel pharmacological
group. In rodents,
CCK-B antagonists
appear
to be potent anxiolytics
(32); human studies are planned.
These agents also appear to have the ability for blocking
withdrawal
from benzodiazepines
(33) or alcohol (34). The
CCK-B antagonists
appear to be relatively
nonsedating,
and apparently
do not produce dependence or withdrawal
after chronic administration
(32). Thus, they may represent an alternative treatment for both alcohol and benzodiazepine
dependence
if future research
confirms the
promising early data in this area. Mditionally,
because
long-term treatment
is required for many of the anxiety
disorders, these agents may have some advantages over
the existing long-term treatments for anxiety disorders,
although considerable research is required to ascertain
this.
In summary, the effects of the CNS cholecystokinin
system in mediating
anxiety
appear to be expressed predominantly through the CCK-B receptors. The availabifity
of
selective antagonists
for CCK receptors has allowed for
initial studies to test appropriate
hypotheses
generated
from the preclinical and clinical studies to date. New therapeutic agents may evolve from this line of research,
which could significantly
improve our ability to treat various psychiatric
and substance abuse disorders. The next
decade should provide interesting
and clinically relevant
information
regarding the role of CCK and CCK antagonists in anxiety and in the treatment of anxiety disorders.
References
1. Vancerhaeghen J-J, Signeau JC, Gepts W. New peptide in the
vertebrate
CNS interacting
with antigastrin
antibodies. Nature
1975;257:604-5.
2. Moran TH, Robinson PH, Goidrich MS. McHugh PR. Two brain
cholecystokinin receptors: implications for behavioral
actions.
Brain Roe 1986;362:175-9.
3. Hill DR, Singh L, Boden P, Pinnick R, Woodruff GN, Hughes J.
In: Cooper ST, Dourish CD, Iversen SD, eds. Multiple
cholecystokinin in the eNS. Oxford: Oxford University
Press, 1992:57-76.
4. Della-Ferra
MA, Bailey CA. Cholecystokinin
octapeptide: continuous picomole injections into the cerebral ventricles of sheep
suppress feeding. Science 1979;206:471-3.
5. Bradwejn J, de Montigney C. Benzodiazepines
antagonize
cholecystokinin-induced
activation of rat hippocampal
neurons.
Nature 1984;312:363-4.
6. Bradwejn J, de Montigny
C. Effects of PK 8165, a partial
benzodiazepine
receptor agonist, on cholecystokinin-induced
activation of hippocampal pyramidal neurons: a microiontophoretic
study in the rat. Eur J Pharmacol 1985;112:415-8.
7. Fekete M, Lengyel A, Hegedus B, Penke B, Zarandy M, Toth
GK, Telegdy G. Further analysis of the effects of cholecystokinin
octapeptide on avoidance in rats. Ear J Pharmacol 1984;98:79-91.
8. Harro J, Vasar E, Bradwejn J. Cholecystokinin in animal and
human research on anxiety. Trends Pharm Sci 1993;14:244-9.
9. Ervin F, Palmour H, Bradwejn J. A new primate model for panic
disorder [Abstract]. New Orleans: New Research Program and Abstracts, 144th meeting Am Psychiatric Assoc, May 1991: NR216.
10. Palmour H, Ervin F, Bradwejn J, Howbert J. The anxiogenic
and cardiovascular
effects of CCK-4 are blocked by the CCK-B
receptor antagonist
LY262 691 [Abstract 637.1]. Soc Neurosci
1991;17:1602.
11. Hendiy SHC, Jones EG, Defilipe J, Schmechell D, Brandon D,
318 CUNICAL CHEMISTRY, Vol. 40, No. 2, 1994
Emson PC. Neuropeptide-containing
neurons of the cerebral cortex
are also GABAergic. Proc Natl Acad Sci USA 1984;81:6526-30.
12. Harro J, Vasar E. Long-term benzodiazepine treatment
produces changes in cholecystokinin
receptor binding in rat brain.
Ear J Pharmacol 1990;180:77-83.
13. Paudice P, Ratieri M. Cholecystokinin release mediated by
5-HT3 receptors in rat cerebral cortex and nucleus accumbens. Br
J Pharmacol
1991;103:1790-4.
14. Harro J, Jossan SS, Oreland L. Changes in cholecystokinin
receptor binding in rat brain after selective damage of locus
ceruleus projections by DSP-4 treatment. Naunyn-Schmiedeberg
Arch Pharmacol 1992;346:425-31.
15. Phillipp E, Wilckens T, Friess E, Platte P, Pirke KM. Cholecystokinin, gastrin, and stress hormone responses in marathon
runners. Peptides 1992;13:125-8.
16. de Montigny C. Cholecystokinin tetrapeptide induces panic-like
attacks in healthy subjects. Arch Gen Psychiatry 1989;46:511-7.
17. Bradwejn J, Koszycki D, Couteoux du Tertre A, Bourin M,
Palmour R, Ervin F. The cholecystokinin
hypothesis of panic and
anxiety disorders [Review]. J Psychopharmacol 1992;6:345-51.
18. Bradwejn J, Koszycki D, Metterissian
G. Cholecystokinintetrapeptide induced panic attacks in patients with panic disorder.
Can J Psychiatry 1990;35:83-5.
19. Bradwejn J, Koszycki D, Shriqtu C. Enhanced sensitivity
to
cholecystokinin
tetrapeptide
in panic disorder. Arch Gen Psychiatry 1991;48:603-10.
20. Bradwejn J, Koszycki D. Comparison of C02-induoed panic
attacks with cholecystokinin-induced
attacks in panic disorder.
Prog Neuropsychopharmacol
Biol Psychiatry 199 1;15:237-9.
21. Bradwejn J, Koszycki D, Dutertre AC, Van Megan H, den
Boer J, Westenberg
H, et al. L-365,260,
a CCK-B antagonist,
blocks CCK-4 in panic disorder [Abstract]. Charleston, SC: Anxiety Disorders Assoc of America annual meeting, March 1993.
22. Abelson JL, Nesse RM. CCK-4 and panic [Letter]. Arch (Inn
Psychiatry 1990;47:395.
23. Abelson JL, Nesse RM. Neuroendocrine,
cardiovascular,
and
behavioral
responses to a cholecystokinin
receptor agonist in
patients with panic disorder [Abstract]. Charleston, SC: Anxiety
Disorders Assoc of America annual meeting, March 1993.
24. Gorman J, Liebowitz MR, Fyer AJ, Stein J. A neuroanatomical
hypothesis for panic disorder. Am J Psychiatry 1989;146:148-61.
25. Branchereau
P, Bohme GA, Chanipagnat
J, Morm-Surun
M-P, Durieux C, Blanchard JC, et al. Cholecystokinin
A and
cholecystokinin
B receptors in neurons of the brainstem solitary
complex of the rat: pharmacologic identification.
J Pharm Exp
Ther 1992;260:1433-40.
26. Lydiard RB, BallengerJC, Laraia MT, Fossey MD, Beinfeld MC.
CSF cholecystokinin concentrations in patients with panic disorder
and normal comparison subjects. Am J Psychiatry 1992;149:691-3.
Denavit-Soubie
M, Hurle MA, Morin-Suryn
MP, Soutz AS,
Champagnat
J. The effect of cholecystokinin-8
on the nucleus
tractus solitarius. Ann NY Aced Sci 1985;48:375-84.
28. Lydiard RB, Zealberg J, Fossey MD, Beinfeld MC, Ballenger
JC. CSF cholecystokinin octapeptide in OCD and normals [Abstract]. San Juan, PR: American College of Neuropsychopharmacology, December 1992.
29. Lydiard RB, Brewerton TD, Fossey MD, Laraia MT, Stuart G,
Beinfeld MC, Ballenger JC. CSF cholecystokinin
octapeptide in
patients with bulimia nervosa and normal comparison subjects.
Am J Psychiatry 1993;150:1099-101.
30. Geraciotti TD, Liddle HA. Impaired cholecystokinin
secretion
in bulimia nervosa. N Engl J Med 1988;319:683-8.
31. Woodruff GN, Hughes J. Cholecystokinin antagonists.
Ann
Rev Pharmacol Toxicol 1991;31:469-501.
32. Hughes J, Boden P, Costall B, Domeney A, Kelley E. Development of a class of selective cholecystokinin receptor antagonists
having potent anxiolytic activity. Proc Natl Acad Sci USA 1990;
27.
87:6728-32.
33. Helton D, Rasmussen
K, Berger J, Scearce E. The selective
cholecystokinin-B
(CCK-B) antagonist
LY288513 attenuates
increases in sensorimotor
reactivity from withdrawal from chronic
diazepam [Abstract]. Chathain, MA. CCK ‘93, May 1993.
34. Singh L, Hughes J, Field M, Woodruff GN. The effects of the
CCK-B receptor antagonist
CI-988 on withdrawal
from chronic
alcohol treatment
[Abstract]. Keystone, CO: Committee on Problems of Drug Dependence, June 1992.