Effect of valproate and pregabalin on human anxiety-like behaviour in a randomised controlled trial

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1 Bach et al. Translational Psychiatry (2018) 8:157 DOI /s Translational Psychiatry ARTICLE Effect of valroate and regabalin on human anxiety-like behaviour in a randomised controlled trial Dominik R. Bach 1,2,3, Christoh W. Korn 1,2,4, Johanna Vunder 1,2 and Antonia Bantel 1,2 Oen Access ():,; ():,; ():,; ():,; Abstract Valroate is an anticonvulsant drug with strong reclinical evidence for reducing anxiety behaviour in rodents but no clear clinical evidence. To motivate clinical trials, we here investigate the use of valroate in a translational human model of anxiety behaviour. In a double-blind, randomised, lacebo-controlled trial, n = 118 healthy articiants layed a reviously validated aroach/avoidance conflict comuter game to measure anxiety-like behaviour, while under 400 mg valroate, under 200 mg of the established anxiolytic/anticonvulsant regabalin, or under lacebo. Saccadic eak velocity and subjective ratings were assessed to control for drug-induced sedation. Comared to lacebo, valroate and regabaline were anxiolytic in the rimary outcome, and several secondary outcomes. Bayesian model comarison decisively demonstrated no differences between the two drugs. Subjective and objective sedation was significantly more ronounced under regabalin than valroate, but did not exlain anxiolytic effects. We demonstrate acute anxiolytic roerties of valroate in healthy humans. Both drugs have similar anxiolytic roerties at the doses used. Valroate is less sedative than regabalin. Our results suggest clinical trials on the use of valroate in anxiolytic treatment. More generally, we roose a strategy of screening drugs in human reclinical models that can directly be comared across secies, such as the aroach/avoidance conflict comuter game used here. This aroach could thus facilitate translational anxiety research. Introduction Rodent anxiety aradigms eliciting aroach/avoidance conflict are often used as reclinical models of anxiety disorder 1. They have successfully enabled screening and develoment of acutely anxiolytic drugs such as a range of benzodiazeines and other anticonvulsants, all of which act via GABAergic athways. Of the many nonbenzodiazeine drugs tested in rodents, few have made it to the clinic 2, and this calls for an imroved strategy of drug evaluation 3,4. A discreancy between re-clinical and clinical effectiveness could be due to limitations of the Corresondence: Dominik R. Bach (dominik.bach@uzh.ch) 1 Clinical Psychiatry Research, Deartment of Psychiatry, Psychotheray, and Psychosomatics, Psychiatric Hosital, University of Zurich, 8032 Zurich, Switzerland 2 Neuroscience Center Zurich, University of Zurich, 8057 Zurich, Switzerland Full list of author information is available at the end of the article. rodent models, but also secies differences in neurotransmitter systems and signalling athways. Ideally, research in reclinical human models with cross-secies comarability 5,6, as comarative intermediate ste, could motivate, or discourage, the large-scale effort of clinical drug testing. Pregabalin is an examle anticonvulsant that has, after initial rodent exeriments 7, successfully been translated to the clinic in various trials Valroate, on the other hand, is not in standard clinical use for anxiety disorders 17 desite strong evidence for its anxiolytic roerties in rodent tests It acts via a athway different from benzodiazeines 19,20, and lacks otential for tolerance 23, indicating its feasibility for rolonged use. Beyond ilot studies 27, and trials with biolar atients and comorbid anxiety 28,29, only one small randomised control trial (RCT) exists for use in generalised anxiety disorder 30. The The Author(s) 2018 Oen Access Thisarticleislicensedundera CreativeCommons Attribution 4.0 InternationalLicense, which ermitsuse, sharing, adatation, distribution and reroduction in any medium or format, as long as you give aroriate credit to the original author(s) and the source, rovide a linktothecreativecommons license, and indicate if changes were made. The images or other third arty material in this article are included in the article s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article s Creative Commons license and your intended use is not ermitted by statutory regulation or exceeds the ermitted use, you will need to obtain ermission directly from the coyright holder. To view a coy of this license, visit htt://creativecommons.org/licenses/by/4.0/.

2 Bach et al. Translational Psychiatry (2018) 8:157 Page 2 of 10 Table 1 Sex Samle characteristics Placebo grou Valroate grou Pregabalin grou 20 male male male 19 female female female Mean ± SD Mean ± SD Mean ± SD Age ± ± ± STAI X ± ± ± STAI X ± ± ± BDI 3.78 ± ± ± VAS overall 1.72 ± ± ± 2.71 <0.001* VAS sedation 2.81 ± ± ± 2.83 <0.001* VAS stimulation 2.77 ± ± ± VAS dizziness 0.92 ± ± ± 3.00 <0.001* PSV re ± ± ± PSV ost ± ± ± * Threat rating 51.3 ± ± ± Threat reference 1.48 ± ± ± STAI X1 trait anxiety score, STAI X2 state anxiety score, BDI deression score, VAS visual analogue scale, administered immediately before the comuter game, PSV eak saccadic velocity from a saccade task before (re) or after (ost) the comuter game, Threat rating exlicit rating of the wake-u robabilities immediately after the comuter game, averaged over the three redators (see Table S5 for an analysis of the individual threat levels), Threat reference most referred threat level from three air-wise comarisons (1: low, 2: medium, 3: high), -value for the omnibus main effect from a 3-level (Placebo, Valroate, Pregabalin) one-way ANOVA See Table S6 for a covariate analysis accounting for the grou differences in VAS and PSV current study sought to answer the question whether valroate has similar acutely anxiolytic roerties as regabalin in humans. To this end, we caitalised on a reclinical human anxiety model 31. In this behavioural task, articiants forage for monetary tokens in successive eochs under threat of a virtual redator that can take away all collected tokens. This task exlicitly its aroach toward rewards (monetary tokens) against avoidance of unishment (cature by redator and loss of reviously collected tokens). It thus shares features with several rodent anxiety tests, which are sensitive to benzodiazeines and hiocamus lesions 32. Our model is not intended to differentiate individuals with or without anxiety disorder, but to temorarily elicit anxiety behaviour in healthy humans. It thus allows focusing on one, ossibly transdiagnostic, dimension of sychoathology, in line with calls for abstraction from articular diagnostic frameworks 33. Normatively, as the number of collected tokens increases over an eoch of our task, otential loss increases, and articiants should become more cautious by retreating to the safe lace. We have reviously shown that this intra-eoch adatation of behaviour is reduced under treatment with lorazeam 34 as well as after hiocamus 31 and amygdala 34 lesions. In our revious studies we comared seven measures of intra-eoch adatation and found that resence in safe lace best searated lorazeam from lacebo 34, and also searated atients with hiocamal 31 and amygdala 34 lesions from control articiants. Hence, resence in safe lace was chosen as rimary outcome, and the linear drug time interaction as a riori contrast. We hyothesised that both regabalin and valroate would reduce the rimary outcome in the a riori contrast. Materials and methods Particiants Particiants were recruited from the general oulation (n = 119; 40 er lacebo and regabalin grou, 39 in valroate grou). One articiant in the regabalin grou did not comlete the study due to vomiting immediately after drug ingestion, such that n = 118 individuals were included in the final analysis. The grous did not differ in age, gender, or baseline ersonality measures (Table 1). All articiants were screened for hysical and mental health conditions by a hysician (see Table S1 for inclusion and exclusion criteria). The study was conducted in accord with the Declaration of Helsinki and aroved by the governmental research ethics committee (Kantonale Ethikkomission Zurich, KEK-ZH ) and by the Swiss Agency for Theraeutic Products (Swissmedic, 2016DR2060). All articiants gave written informed consent using a form aroved by the ethics committee. The study was re-registered at the rimary German Clinical Trials Register (DRKS ) and at the Swiss Federal Comlementary Database (KOFAM; SNCTP ), and conducted at the University of Zurich between 09 June 2016 and 16 Setember Power analysis To determine required samle size, we conducted a ower analysis (using G*ower 35 ) based on our revious study on lorazeam. This study revealed, in the lanned rimary outcome and contrast for the resent study, an effect size estimate of artial η 2 = , based on t = 5.34 and df residual = 798. The non-shericity correction for residual degrees of freedom in this error stratum was Greenhouse Geissers ε = , and the average correlation between data oints from the same subject in this error stratum was r = Based on these samle values, to achieve 80% ower at a tye I error threshold of α = 0.05, a samle size of n = 37 er grou was needed. We set our target samle size at n = 40 er grou to allow for attrition.

3 Bach et al. Translational Psychiatry (2018) 8:157 Page 3 of 10 Study medication Our study medication was 400 mg valroic acid (corresonding to 500 mg sodium valroate), sulied in owder form from Katwijk chemie bv (Katwijk, The Netherlands), and 200 mg regabalin, brand name Lyrica (Pfizer, Zurich). Study dose for valroate was based on the recommended starting single dose (corresonding to half a daily dose) to minimise side effects. Pregabalin dose was based on revious work in healthy humans 36,37 and within the range of the manufacturer s daily dose recommendation on the Swiss market for treatment of GAD ( mg er day in 2 3 single doses). According to manufacturers brochures, eak lasma concentrations are reached at aroximately min (valroate) and 60 min (regabalin) after oral administration; the drugs half-lifes are aroximately 10 h (valroate) and 6.5 h (regabalin). A GMP-licensed harmacy (Kantonsaotheke Zürich) manufactured four casules er articiant containing mg valroate, regabalin, and 3 mannitol or 4 mannitol (lacebo). The harmacy randomised and blinded the study medication, searately for male and female articiants. Randomisation code was broken after the last articiant comleted the study, and after all data were checked for consistency. Procedure Screening visit 1 (day 7 to day 1) Exclusion criteria were checked via medical/sychiatric examination, and blood/urine test (Fig. 1a, Sulemental Methods). Drug visit 2 (day 0) Particiants filled in the State-Trait Anxiety Inventory 38 and Beck s Deression Inventory 39 before ingesting study medication. During a 100-min metabolisation time, they were ket under surveillance of study staff. Particiants sent this time ad libitum, and were allowed to eat snacks but no meals. Next, we measured saccadic eak velocity (Sulemental Data), and articiants filled in visual analogue scales (VAS) to record subjectively erceived overall drug effect (I feel substance effect), sedation (I feel dazed/sleey), stimulation (I feel activated/awake), and dizziness (I feel dizzy). One hundred twenty minutes after drug ingestions, they started laying the aroach/ avoidance comuter game, which lasted around 1 h. Afterward, we again measured saccadic eak velocity. Behavioural AAC aradigm Particiants comleted 240 eochs of our reviously described AAC task 31,34, resented using the MATLAB toolbox Cogent ( In each eoch, articiants collected monetary tokens on a grid under threat of being attacked by a redator, which resulted in the loss of all tokens collected in the given Fig. 1 Exerimental design. a Study rocedure. b Behavioural aroach-avoidance conflict (AAC) comuter game. A human layer (green triangle) is foraging for tokens (yellow rhombi), which contribute to financial reimbursement at the end of the game. At any time, 10 tokens are resent and are relaced in random osition when collected. Collected tokens are shown in the uer left corner, above the grid. Meanwhile, a redator (grey circle) is inactive in a corner of the grid, and can attack the human layer at any given time according to three robabilities secified by the frame colour. To avoid being caught by the redator, the layer can seek shelter in a safe lace. Presence in the safe lace constitutes the rimary outcome measure. The safe lace is always diagonal to the initial redator osition. During the chase hase, when the redator wakes u, the frame colour turns red. All tokens from this eoch are lost when the layer is caught eoch (Fig. 1b). One corner of the grid was a safe lace, in which the redator could not attack. Location of the safe lace was randomised on each eoch. Tokens At all times, 10 tokens were uniformly distributed on the grid, and every 2 s one of the tokens changed its osition randomly. Collected tokens were relaced on the grid, and their number dislayed above. Predator The redator was initially inactive in the corner diagonal to the safe lace. The redator could become active and chase articiants any time. Colour of the frame around the grid (blue, urle, orange) indicated three distinct redator wake-u robabilities (0.2, 0.5, and 0.8), which articiants learned to distinguish. Particiants started either in the same lace as the redator (which we

4 Bach et al. Translational Psychiatry (2018) 8:157 Page 4 of 10 term active condition) or in the safe lace, oosite the redator (which we term assive condition here). Notably, all rounds entailed going out onto the grid to collect tokens, and over the course of an eoch, behaviour becomes comarable for the two conditions (see Fig. S1). Movements on the grid Particiants coordinated their movements by ressing the four comuter keyboard arrow keys. No diagonal movements were ossible. Particiants could move at a maximum seed of 10 grid blocks er second. All three redators had the same seed of 40 grid blocks er second. Thus, articiants could try to escae an active redator by retreating to the safe lace but the redator moved four times faster, and thus escae was only ossible if articiants were close to the safe lace. Eoch duration Eochs lasted 3 15 s (drawn from a uniform distribution with stes of 1.7 s). There was a 3 s countdown with a review of the grid layout before each eoch, during which the layer could not move. This was meant to facilitate orientation with resect to starting lace/redator osition. After the re-determined eoch duration, the redator either woke u, or the next eoch started. 240 eochs were divided into five blocks with short selfaced breaks. Post-task questions Particiants rated on a VAS (ranging from 0% to 100%) the wake-u robability and wake-u latency of the three different redators. Bonus eoch Finally, articiants were given the choice to select the redator that they would like to face in a final bonus round. The selection rocess entailed three consecutive air-wise comarisons between the redators. Payment At the end of the game, the average number of tokens from nine randomly selected eochs, lus the bonus eoch, was transformed into a monetary reimbursement that was added to the constant show-u fee. Outcome measures Proortion of resence in safe lace (the only grid block which the redator could not enter) was chosen as rimary outcome, and the linear drug time interaction as a riori contrast. As in revious studies 31,34 we additionally reort six further measures as secondary outcomes, Bonferroni-corrected for six comarisons: (1) distance (as the crow flies) from threat (i.e., from the redator), (2) distance from nearest wall, (3) resence in safe quadrant (i.e., the quarter of the grid surrounding the safe lace), (4) resence in threat quadrant (i.e., quarter of the grid surrounding the redator osition), (5) token collection, and (6) seed when outside safe lace. Note that in our revious study on lorazeam, resence in safe quadrant was chosen as rimary outcome 34. This choice had been based on a receding hiocamus lesion study 31, but it turned out that resence in safe lace better searated lorazeam from lacebo 34. As auxiliary measures, we analyse latency to forage after eoch start, and latency to flight after redator wake-u; catch rates, and the average number of tokens retained at the end of each eoch, including the chase hase; subjectively rated wake-u robabilities and wake-u times of the three different redators, and articiants references in air-wise comarison of the three redators. Statistical analysis We averaged articiants ositions on the grid within 1 s bins, and then averaged across eochs, for each articiant, each condition, and time bin. Since eoch duration was variable, more data were available for earlier than for later time bins. Our factorial design included a between-subjects factor (Placebo/Valroate/Pregabalin) and three within-subjects factors: threat level (wake-u robability, low/medium/high), task (active/assive start), and time (15 time bins of 1 s duration). For some measures (token collection and seed when on grid), some articiants had no data values in the final time bins (as they were in the safe lace for all trials during these time bins), and these time bins were removed for analysis. We used the software ackage R (function aov) to erform full multistratum reeated-measures ANOVA model with Greenhouse Geisser corrected degrees of freedom. We reort the following a riori contrasts: (valroate vs. lacebo) time, (regabalin vs. lacebo) time. To test for drug differences, we also assess the third, nonindeendent contrast (regabalin vs. valroate) time. To confirm drug equivalence, we reort a Bayesian model comarison between a model with one redictor er drug, and reduced (non-nested) model with one redictor for lacebo, and one for the two drugs. We comute Bayesian information criterion (using the R function BIC) and interret an absolute BIC difference >6 as decisive 43. Code availability All codes used to generate the results in this manuscrit are fully available from the authors. Results Two hours after ingesting valroate, regabalin, or lacebo, articiants erformed the AAC comuter game (Fig. 1b). Both valroate and regabalin significantly reduced the rimary outcome (a riori contrasts:

5 Bach et al. Translational Psychiatry (2018) 8:157 Page 5 of 10 Fig. 2 Effect of valroate and regabalin on rimary and secondary outcomes. Line grahs show evolution of outcome measures over 15 s eochs, evaluated in 1 s time bins. Inset bar grahs reflect the a riori contrast and show estimated change over time (linear fixed-effects coefficients ± standard error) for the three conditions. Inset scatter lots show change over time for individual articiants, estimated in single-articiant models fitted ost hoc; these have no relation to the statistical hyothesis test and are shown for illustrative uroses. a Proortion of time sent in the safe lace (see Fig. 1b) linearly increases over time, and this increase is reduced in articiants under valroate or regabalin as comared to lacebo (linear drug time interaction, see Table 2). b Six secondary outcome measures. There is no significant difference between the two drugs in any measure, and Bayesian model comarison favours a model in which they have the same imact as comared to lacebo. See Fig. S1 for a comarison with lorazeam. VPA valroate, PGB regabalin, PLC lacebo. *: significant linear drug time interaction (for secondary outcomes after Bonferroni correction) valroate: F (1, 185) = 7.56, = 0.007, artial η 2 = 0.005; regabalin: F (1, 185) = 16.08, = 0.001, artial η 2 = 0.010). Figure 2a shows that as intra-eoch time assed, articiants under lacebo sent increasingly more time in the safe lace, and this linear change over time was reduced in articiants under both drugs. In Bonferroni-corrected secondary outcomes, valroate reduced loss adatation in distance from threat, while regabalin reduced loss adatation in distance from threat, resence in threat quadrant, and seed when on grid (Fig. 2b). Exloratory analyses of the other error strata are summarised in Table 2. At the same time, articiants behaviour in the lacebo grou was generally similar to the behaviour of healthy articiants in our revious reorts (see Table S2 and Fig. S1). Next, we directly comared the effect of regabalin and valroate in a further non-indeendent contrast (Table 2). No significant difference between the two drugs in their

6 Bach et al. Translational Psychiatry (2018) 8:157 Page 6 of 10 Table 2 Comarison of lacebo, valroate, and regabalin Presence in safe lace* Distance from threat Distance from walls Presence in safe quadrant Presence in threat quadrant Tokens er second Seed when on grid Valroate Pregabalin Valroate threat omnibus 3.43* Valroate threat linear 2.49* Pregabalin threat omnibus Pregabalin threat linear Valroate task Pregabalin task Valroate time omnibus Valroate time linear 2.75* 2.87* Pregabalin time omnibus Pregabalin time 4.01* 4.56* * 3.80* * linear.001 < <.001 < Pregabalin vs. valroate time linear Valroate threat time omnibus Valroate threat time linear Pregabalin threat time omnibus Pregabalin threat time linear * 3.85* 3.62* * <.001 <.001 < * * * Results are shown from a 3 (Grou: Placebo, Valroate, Pregabalin) 3 (Threat: Low, Medium, High) 2 (Task: Active/Passive) 15 (Time bins of 1 s each) ANOVA. The table lists F-values for omnibus effects and signed t-values for olynomial contrasts and for the main effects of drug and task. -values were comuted using Greenhouse Geisser corrected degrees of freedom. Significant -values after Bonferroni correction (rimary outcome: α =.05; secondary outcomes: α =.05/ ) are marked with asterisk. Signs of t-values are coded as higher-deendent values for drug vs. lacebo, higher levels of threat, later time oints, and assive vs. active. * rimary outcome. a riori contrasts. non-indeendent direct comarison of regabalin and valroate in the a riori contrast (see also Fig. 2 and Fig. S1) imact on linear time adatation emerged. To demonstrate drug equivalence, we then conducted a Bayesian model comarison. For the a riori contrast in all outcomes, model evidence decisively favoured a model with a common redictor for both drugs (Table S3), i.e., there was decisive evidence (BIC difference >6) for drug equivalence. In two erformance measures, catch rates and average number of tokens retained at the end of each eoch (including chase hase), no significant grou difference emerged ( >.1, Table S4). Thus, all articiants maximised their token collection, but by doing so they used slightly different strategies. There was no grou difference in exlicit ratings of redator robability, or reference for the three redators (Table S4, all s >.1). After including these measures as covariates (together with their time interaction) into the initial model, the significance of linear drug time effects remained unchanged (Table S5). Next, we were concerned that drug-induced sedation might exlain the imact of the drugs on the rimary and secondary outcome measures. Latency to escae when the redator woke u was different between the study grous ( =.029; Table S4), ossibly indicating anxiolysis or sedation. Indeed, self-ratings of overall drug effect and sedation were higher for regabalin than lacebo (Table 1,

7 Bach et al. Translational Psychiatry (2018) 8:157 Page 7 of 10 overall: t (68) = 6.7, <.001; sedation: t (77) = 5.2, <.001) or valroate (overall: t (71) = 6.4, <.001; sedation: t (74) = 4.9, <.001). Furthermore, saccadic eak velocity, a sensitive measure of drowsiness induced by GABAergic drugs, was lower for regabalin than lacebo (t (75) = 2.9, =.005) or valroate (t (71) = 2.3, =.033) when measured immediately after the game (Table 1). This is why we included all self-ratings (overall drug effect, sedation, stimulation, dizziness) and saccadic eak velocity before and after the game, into our model as covariates, together with their time interaction. Significance of the a riori contrasts was unchanged in all rimary and all secondary outcome measures (Table S5). In sum, although regabalin aeared to induce relevant sedation in self-ratings and objective measures, we found no evidence that the imact of valroate and regabalin on loss adatation in our task could be exlained by sedation. Further exloratory analysis revealed that females resonded more strongly to regabalin than males in rimary and one secondary outcome measures while there was no such difference for valroate (Table S6). We note our study was not owered to detect sex-secific drug effects. Finally, we sought to directly comare the drug doses used here with the effect of 1 mg lorazeam in a revious study 34 (Table S7 and Fig. S1). All three drugs combined showed an anxiolytic effect on rimary outcome as well as on distance from threat, resence in safe quadrant, resence in threat quadrant, and seed when on grid. Lorazeam turned out to have a significantly stronger effect than the other two drugs on rimary outcome as well as distance from walls, tokens er second, and seed when on grid. In most of these measures, all three drugs were (near-) significantly different from lacebo. However, distance from walls (otentially measuring thigmotaxis, relating to agorahobia 44 ) was ronouncedly influenced by lorazeam and not by regabaline or valroate. Thus, it aears not only that the lorazeam dose used was more anxiolytic than the regabalin or valroate dose, but also that the drugs may somewhat differ in their secific attern of anxiolytic influences. Discussion Valroate is acutely anxiolytic in various rodent tests but evidence for its efficacy in anxiety disorders is limited to a ilot study 30. To facilitate further clinical research, we here erformed an intermediate comarative research ste 5 and asked whether valroate is acutely anxiolytic in healthy humans. As a main finding, valroate had an anxiolytic effect on the rimary and one secondary outcome measure. There was no significant difference between valroate and regabalin in our a riori contrast in any outcome measure. Bayesian model comarison decisively showed equivalence of the two drugs. Thus, we found no indication of an anxiolytic difference between the two drugs, but sedative side effects were far more ronounced under regabalin than valroate. Notably, regabalin dose was chosen based on revious studies in healthy humans 36,37 and is in the range of the recommended daily doses for treatment of GAD. To minimise side effects, valroate dose was selected more cautiously and is in the range of a half daily starting dose for eilesy. It is ossible that higher doses of valroate have a stronger anxiolytic action but would also elicit more sedative side effects. At the doses used here (200 mg regabalin, 400 mg valroate), a direct comarison with a revious study 34 revealed that these drugs were less anxiolytic than 1 mg lorazeam. Furthermore, different from lorazeam, they did not influence thigmotaxis, a behaviour sometimes associated with agorahobia 44. A revious RCT comared mg valroate (Deakine chrono) over 6 weeks with lacebo for the treatment of GAD in n = 74 atients 30. This trial found significantly higher resonse rates (50% HAMD reduction) in valroate vs. lacebo-treated atients. As a limitation, lacebo resonses in this study were much lower than in other studies, e.g., in many RCTs with regabalin. Until today, no larger hase II studies have been conducted on valroate to relicate this ilot trial. While our results suggest acutely anxiolytic roerties of valroate, the single-dose design used here is not directly comarable to rolonged treatment over several weeks or months. Consequently, we cannot directly make statements on clinical effectiveness, which will require new clinical trials. To test anxiolytic roerties, we used our recently established human aroach/avoidance conflict aradigm 31,34,45,46. This aradigm is designed to reflect rodent conflict test and is sensitive to anxiolytic action of lorazeam 34. It is thus different from tests designed to elicit anxiety feelings, such as ublic seaking anticiation, for which no unambiguous demonstration of sensitivity to benzodiazeines exists 47. As a limitation, it is not clear to what extent the recise attern of benzodiazeine effects in conflict tests reflects their clinical efficacy. Thus, while our aroach is likely to reveal drugs that have effects similar to benzodiazeines in our conflict test, they are not guaranteed to have the same effect as benzodiazeines in a clinical condition. This concern could ossibly be mitigated by investigating valroate in other reclinical anxiety tests, articularly in tests that are concetually different from rodent aroach/avoidance conflict. While it has been noted that our task uses financial incentives rather than real threat 48 (such as mild electric shocks or unleasant images and sounds 49,50 ), its immersive nature may be effective enough to create a situation comarable with real threat. Secifically, it is the only resently

8 Bach et al. Translational Psychiatry (2018) 8:157 Page 8 of 10 available human aroach-avoidance aradigm validated with anxiolytic drugs and lesion models. Our aradigm was designed to induce behavioural strategies that resemble those seen in clinical anxiety states, such as assive avoidance and behavioural inhibition. Because the diagnosis of anxiety disorders rimarily relies on atients introsective assessment, i.e., symtoms rather than signs 5, it would be useful to assess the feelings induced in healthy ersons while being engaged in the task resented here, which was not the focus of the current study. At the same time, it may be informative to assess the behavioural strategies that GAD atients use in our task. Interestingly, the anxiolytic effects of lorazeam, regabalin, and valroate are robably mediated via the GABAergic system, but by different mechanisms of action. Lorazeam, like other benzodiazeines, binds allosterically to the GABA (A) recetor and thus increases the imact of GABA 51. The other two drugs increase GABA levels, but by less well understood mechanisms 52. Pregabalin does not bind to GABA recetors but to the α 2 δ-1 subunit of voltage-gated calcium channels, and this binding is required for the anxiolytic roerties of the drug 53. Valroate inhibits succinic semialdehyde dehydrogenase, such reducing the degradation of succinic semialdehyde, which inhibits the GABA-degrading enzyme GABA transaminase 54,55. It also acts on non- GABAergic transmission by inhibiting voltage-gated Na channels, and several further mechanisms of action have been seculated, including at the genomic level, but without clear evidence for their relevance even in the main indications for valroate, namely, eilesy and biolar disorder 55. Other antieiletic drugs otentially acting via GABA-mediated mechanisms are gabaentin, vigabatrin, and tiagabin 52, which are therefore candidate drugs for future reclinical tests. Once the relevant athways mediating the anxiolytic action of regabalin and valroate are elucidated, this could lead to the develoment of new anxiolytic comounds. We roose all of these substances could be evaluated in our human re-clinical model, as this would render an investment into large-scale clinical studies more feasible. One concern sometimes raised with resect to rodent aroach/ avoidance tests is their sensitivity to GABAergic but not other anxiolytic substances such as antideressants 4. Investigating the sensitivity of our human model to non- GABAergic anxiolytic as well as non-anxiolytic substances could facilitate the screening of new drugs. Desite their well-known side effects and addiction otential, benzodiazeines are still commonly rescribed for GAD (e.g., estimated rescrition rates in 2002 across the US: 38% 56 ) desite the availability of alternatives such as SSRIs, regabalin, and sychotheray. While there may be many reasons for this, it could indicate subotimal resonse rates to these alternative treatments. A metaanalysis across different drug treatments found resonse rates between 40 and 75%, with a mean of 55% 57. Similarly, a recent industry-sonsored combined analysis of regabalin trials found a resonse rate (at trial endoint) of around 60% 58. This leaves significant room for imrovement. It would be interesting whether atients that do not resond to sychotheray, regabalin, or SSRIs, could benefit from valroate. To summarise, our study demonstrates acutely anxiolytic roerties of valroate in healthy humans, and thus suggests a otential of this drug in the treatment of anxiety disorders. More generally, we furnish a new strategy for testing drugs in translational anxiety research, by harnessing an intermediate comarative model in healthy humans. This model is not suosed to distinguish individuals with our without anxiety disorders by their behaviour in the test, but instead to temorarily elicit a articular dimension of sychoathology in healthy humans. Thus, a validation of this aroach will be the demonstration that effectiveness in the reclinical test redicts clinical efficacy. With this work, we hoe to advance clinical research on new treatments for anxiety disorders. Acknowledgements We thank Alexandra Lüber for hel with data acquisition. This work was funded by the University of Zurich. The Wellcome Centre for Human Neuroimaging is suorted by a strategic grant from the Wellcome Trust [091593/Z/10/Z]. The funders had no role in design and conduct of the study; collection, management, analysis, and interretation of the data; rearation, review, or aroval of the manuscrit; and decision to submit the manuscrit for ublication. Author details 1 Clinical Psychiatry Research, Deartment of Psychiatry, Psychotheray, and Psychosomatics, Psychiatric Hosital, University of Zurich, 8032 Zurich, Switzerland. 2 Neuroscience Center Zurich, University of Zurich, 8057 Zurich, Switzerland. 3 Wellcome Trust Centre for Neuroimaging and Max Planck-UCL Centre for Comutational Psychiatry and Ageing Research, University College London, London WC1 3BG, UK. 4 Institute for Systems Neuroscience, University Medical Center Hamburg-Eendorf, Martinistrasse 52, Hamburg, Germany Authors contributions D.R.B., J.V., and C.W.K. designed the study. J.V., A.B., and D.R.B. conducted the research. D.R.B. and C.W.K. analysed the data. All authors contributed to the final manuscrit. Conflict of interest The authors declare that they have no conflict of interest. Publisher's note Sringer Nature remains neutral with regard to jurisdictional claims in ublished mas and institutional affiliations. Sulementary Information accomanies this aer at (htts://doi.org/ /s ).

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