Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
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.