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. Author manuscript; available in PMC: 2017 Jun 1.
Published in final edited form as: Neuropharmacology. 2016 Jan 12;105:25–34. doi: 10.1016/j.neuropharm.2016.01.017

Effects of Iloperidone, Combined with Desipramine, on Alcohol Drinking in the Syrian Golden Hamster

Jibran Y Khokhar a, Alan I Green a,b,*
PMCID: PMC4873404  NIHMSID: NIHMS754314  PMID: 26796639

Abstract

Alcohol use disorder in patients with schizophrenia dramatically worsens their clinical course, and few treatment options are available. Clozapine appears to reduce alcohol use in these patients, but its toxicity limits its use. To create a safer clozapine-like drug, we tested whether the antipsychotic iloperidone, a drug that combines a weak dopamine D2 receptor blockade and a potent norepinephrine alpha-2 receptor blockade would reduce alcohol drinking, and whether its effect on alcohol drinking could be increased if combined with an agent to facilitate norepinephrine activity. Syrian golden hamsters (useful animal model for screening drugs that reduce alcohol drinking in patients with schizophrenia) were given free access to water and alcohol (15% v/v) until stable drinking was established. Animals (n=6-7/group), matched according to alcohol intake, were treated daily with each drug (iloperidone; clozapine; haloperidol; desipramine [norepinephrine reuptake inhibitor]; with idazoxan [norepinephrine alpha-2 receptor antagonist]) or with a two-drug (iloperidone+desipramine; iloperidone+idazoxan) combination for 14 days. Moderate doses of iloperidone (1-5mg/kg) significantly reduced alcohol drinking (p<0.05) in the hamster, whereas higher doses (10-20mg/kg) did not. In addition, 5 mg/kg of iloperidone reduced alcohol drinking to the same extent as clozapine (8mg/kg), whereas haloperidol (0.2mg/kg) did not. Moreover, iloperidone's effects were enhanced via the addition of desipramine (3mg/kg), but not idazoxan (1.5/3mg/kg). In this animal model, iloperidone decreases alcohol drinking as effectively as clozapine, and desipramine appears to amplify this effect. The data suggest that iloperidone, alone or in combination with desipramine, should be tested in patients with schizophrenia and alcohol use disorder.

Keywords: dual diagnosis, antipscychotic, addiction, animal model

Introduction

Alcohol use disorder (AUD) occurs commonly in patients with schizophrenia (SCZ); 30% of patients drink regularly, and this use significantly worsens the course of schizophrenia (Regier et al., 1990). Although patients with SCZ consume only moderate amounts of alcohol and tend not to be dependent on alcohol (Drake and Mueser, 1996b), AUD in these patients is associated with poor treatment response, treatment non-compliance (Owen et al., 1996), relapse (Drake and Mueser, 1996a; Gupta et al., 1996), violence (Bartels et al., 1991; Swanson et al., 1990) and suicide (Allebeck et al., 1987; Harkavy-Friedman and Nelson, 1997). Most antipsychotic medications do not reduce alcohol drinking in patients with SCZ. However, use of the atypical antipsychotic clozapine (CLOZ) has been associated with reductions in alcohol drinking in patients with SCZ (Drake et al., 2000; Green et al., 2008; Green et al., 1999; Lee et al., 1998; Zimmet et al., 2000). Unfortunately, in clinical treatment programs CLOZ is used sparingly in only the most treatment-resistant patients due to its toxic side-effect profile (e.g., agranulocytosis).

Our group and others have proposed that patients with SCZ may have a deficit in their dopamine (DA)-mediated mesocorticolimbic brain reward circuit functioning (possibly related to reduced DA release in the prefrontal cortex [Slifstein et al., 2015]) that underpins their alcohol use, and that alcohol may transiently improve the functioning of this circuit (Chambers, 2007; Green et al., 1999). Furthermore, we have also proposed that CLOZ, because of its broad-spectrum effects, including its weak DA D2 receptor antagonism (effective at ~45% DA D2 occupancy [Farde et al., 1994; Nordstrom et al., 1995]), potent norepinephrine (NE) α-2 receptor antagonism and ability to increase levels of NE in plasma and brain (in part through a possible NE reuptake inhibition ability (Gulick et al., 2014; Yoshimura et al., 2000)), may also improve the functioning of this circuitry and thereby limit alcohol/other substance use in these patients (Chau et al., 2011; Chau et al., 2010; Chau et al., 2004; Green et al., 2004; Green et al., 1999). We have also noted that typical antipsychotics, such as haloperidol (HAL), are not able to decrease alcohol drinking in patients with SCZ (Green et al., 2004), and we have suggested that this may be, in part, due to their potent dopamine D2 receptor antagonism, which may itself produce a reward deficit (Bedard et al., 2013; Grace, 1991), while CLOZ's reduced DA D2 occupancy does not (Nordstrom et al., 1995).

In this regard, using a Syrian golden hamster model, our lab has explored the development of CLOZ-like drugs by combining drugs that have a similar pharmacological profile to CLOZ. One atypical antipsychotic that has been proposed to possess a CLOZ-like pharmacology is iloperidone (ILOP); ILOP has a similar α-2/D2 receptor antagonism ratio to CLOZ (Kalkman and Loetscher, 2003). We have hypothesized that ILOP, like CLOZ, may also reduce alcohol drinking in the hamster, and may have potential as a treatment for AUD in SCZ, either by itself or in combination with other agents to allow it to have even more of a CLOZ-like action.

The hamster is an appropriate bioassay for AUD in SCZ because: (a) like patients with SCZ, the hamster consumes alcohol on a regular basis and does not develop dependence (Ferris et al., 1998; Harris et al., 1979; Keung et al., 2000); and (b) like patients with schizophrenia, CLOZ reduces alcohol drinking in this animal, whereas HAL does not (Green et al., 2004). We have used the hamster model in previous studies to test the effects of antipsychotic drugs (e.g., risperidone, paliperidone), alone or in combination with a NE reuptake inhibitor, on alcohol drinking (Chau et al., 2015; Gulick et al., 2014; Khokhar et al., 2015). While results from our studies are not in agreement with rat studies assessing the effects of antipsychotics on alcohol withdrawal symptoms (Celikyurt et al., 2011; Uzbay, 2012), possibly due to the lack of demonstrable withdrawal in the hamster (Kulkosky and Cornell, 1979), our findings in the hamster are consistent with reports from human studies (Green et al., 2003; Green et al., 2007), further supporting our use of the hamster model. In this study, we assessed: a) whether ILOP can reduce alcohol drinking in the hamster; b) how the reduction compares to CLOZ; and c) whether ILOP's ability to reduce alcohol drinking can be enhanced via the addition of either the NE reuptake inhibitor desipramine (DMI), or the NE α-2 antagonist idazoxan (IDAZ).

2. Materials and Methods

2.1 Animals

Adult, male Syrian golden hamsters (Mesocricetus Auratus; 100-130g) were purchased from Harlan Inc. (Indianapolis, IN). Animals were housed individually and maintained on a 12 h/12 h light/dark cycle with ad libitum food and water access. Hamsters had free access to two drinking bottles (water and 15% alcohol [v/v]); the two bottles were rotated daily to prevent positional preference. A blinded technician measured fluid intake every 24 hours and food intake and body weight every 48 hours. Once the hamsters reached a stable baseline level of alcohol intake, drug treatment began. All injections were performed at least 2-3 hours prior to the start of the dark cycle to avoid any immediate locomotor effects of the drugs on alcohol intake. Experiments were performed in accordance with the National Institute of Health Guide for the Care and Use of Laboratory Animals (NIH Publications No. 80-23) revised in 1996. All procedures were approved by the Institutional Animal Care and Use Committee (IACUC) at Dartmouth College.

Experiment 1

Sixty-seven hamsters were given access to two bottles (water and 15% v/v alcohol) for 12 days prior to randomization into 8 groups based on baseline alcohol intake (g/kg; n=8-9 per group), which was calculated using the last 4 days of the initial 11-day period of access to alcohol. The groups were subsequently treated daily for 14 days with either: vehicle (VEH); or 0.05, 0.5, 1, 2.5, 5, 10, or 20 mg/kg ILOP. All hamsters received free access to food, water, and alcohol during treatment.

Experiment 2

Sixty-three hamsters were given access to two bottles (water and 15% v/v alcohol) for 12 days prior to randomization into 8 groups based on baseline alcohol intake (g/kg; n=7-8 per group). The groups were subsequently treated daily for 14 days with either: vehicle (VEH); 1 mg/kg, 2.5 mg/kg or 5 mg/kg ILOP; 4 mg/kg or 8 mg/kg CLOZ; or 0.2 mg/kg or 1 mg/kg HAL. Doses of ILOP were based on data from Experiment 1, whereas doses of HAL and CLOZ were based on our previous reports(Chau et al., 2010; Green et al., 2004; Khokhar et al., 2015). All hamsters received free access to food, water, and alcohol during treatment.

Experiment 3

Seventy hamsters were given access to two bottles (water and 15% v/v alcohol) for 12 days prior to randomization into 9 groups based on baseline alcohol intake (g/kg; n=8-9 per group). The groups were subsequently treated daily for 14 days with either: vehicle (VEH); 1 mg/kg or 5 mg/kg ILOP; 1 mg/kg or 3 mg/kg DMI; or each of the 4 combinations of the two drugs. The 1 mg/kg (sub-optimal) dose of ILOP was used in addition to an optimal dose (5 mg/kg) to ensure that the effects of the addition of DMI or IDAZ would be visible and not obscured due to a possible floor-effect. The doses of DMI were chosen based on our previous experiments (Gulick et al., 2014; Khokhar et al., 2015). All hamsters received free access to food, water, and alcohol during treatment.

Experiment 4

Seventy hamsters were given access to two bottles (water and 15% v/v alcohol) for 12 days prior to randomization into 9 groups based on baseline alcohol intake (g/kg; n=7-8 per group). The groups were subsequently treated daily for 14 days with either: vehicle (VEH); 1 mg/kg or 5 mg/kg ILOP; 1.5 mg/kg or 3 mg/kg IDAZ; or each of the 4 combinations of the two drugs. The doses of IDAZ were chosen based on our previous studies in hamsters (Khokhar et al., 2015). All hamsters received free access to food, water, and alcohol during treatment.

2.3 Drugs

CLOZ, HAL, IDAZ and DMI were purchased from Sigma Aldrich (St. Louis, MO), whereas ILOP was purchased from ChemPacific (Baltimore, MD). All drugs were dissolved in 0.5 N acetic acid, with the volume adjusted in the 0.5 M sodium acetate vehicle solution (pH 5.5). All drug and VEH solutions were injected subcutaneously in a volume of 2 ml/kg of body-weight.

2.4 Data analysis

All data analyses were performed using SPSS 21 (IBM Inc., Chicago, IL). Alcohol intake (g/kg), alcohol preference, food-intake (g/kg), and body-weight (g) data were analyzed using a two-way repeated measures analysis of co-variance (RMANCOVA), using time (measured in days) and drug treatment as independent variables and the last four days of alcohol drinking prior to treatment as covariates. The main effects between treatment groups were compared in a pair-wise manner using a least significant difference (LSD) confidence interval adjustment. When the analysis indicated that a significant time by treatment interaction was observed on either alcohol intake or preference, pairwise within-day comparisons between groups were made using the Tukey adjustment to help interpret time by treatment interactions from the RMANCOVAs; adjustment to p-values was carried out separately at each day. Data are expressed as mean (M) ± standard error of the mean (SEM) and significance was set at p<0.05.

Results

Experiment 1: Iloperidone reduces alcohol drinking maximally at moderate doses

We assessed the effects of ILOP on alcohol drinking in the hamster at doses ranging from 0.05 to 20 mg/kg (Figure 1). Overall, a significant effect of time (F(13,715)=5.278 p=0.000) and treatment (F(7,55)=5.278 p=0.000) and a significant time by treatment interaction (F(91,715)=2.452 p=0.000) were observed on alcohol intake. An inverted-U shaped dose response curve was observed with moderate doses of ILOP (1-5 mg/kg) reducing alcohol drinking maximally (Figures 1A, 1C). Pair-wise analyses showed that 0.05 mg/kg ILOP did not reduce alcohol drinking significantly, whereas significant reductions in alcohol drinking were seen at doses ranging from 0.5 and 20 mg/kg ILOP when compared to VEH (* P<0.05). The 2.5 mg/kg dose of ILOP had a trend significance (P=0.06) toward a greater ability to decrease alcohol drinking than the higher (10 or 20 mg/kg) doses of ILOP. Within day post-hoc analyses showed that the 1 mg/kg dose of ILOP differed from VEH on day 14, whereas the 2.5 mg/kg ILOP dose differed from VEH on days 7-11 and 14, and the 5 mg/kg doses of ILOP differed from VEH on days 7 and 10. The 5, 10 and 20 mg/kg doses differed significantly from the 0.05 mg/kg dose on days 2, 7 and 10 whereas the 2.5 mg/kg dose differed from 0.05 mg/kg on days 4, 7, 10-11.

Figure 1. Iloperidone reduces alcohol drinking maximally at moderate doses.

Figure 1

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ILOP (1-5 mg/kg) reduces (A) alcohol intake and (B) alcohol preference in the hamster (mean across all days in baseline or treatment periods ± SEM; * p<0.05 compared to VEH from pair-wise analyses). (C) and (D) represent daily alcohol intake and preference respectively (daily group means ± SEM).

When we assessed the effects of a dose range of ILOP on alcohol preference (Figures 1B, 1D), we found that there was a significant effect of time (F(13,715)=4.051 p=0.000) and treatment (F(7,55)=3.125 p=0.008) and a significant time by treatment interaction (F(91,715)=2.064 p=0.000 were observed on alcohol preference. Pair-wise analyses showed that 0.05 mg/kg ILOP did not reduce alcohol drinking significantly, whereas significant reductions in alcohol preference were seen at doses ranging from 0.5 and 10 mg/kg ILOP when compared to VEH (* P<0.05). Within day post-hoc analyses showed that the 1 mg/kg dose of ILOP differed from VEH on day 14, whereas the 2.5 mg/kg ILOP dose differed from VEH on days 7-9 and 11, and the 5 mg/kg doses of ILOP differed from VEH on days 5 and 9. The 2.5 and 5 mg/kg dose differed significantly from the 0.05 mg/kg dose on day 7.

There was also a significant effect of time (F(13,715)=6.649 p=0.000) and treatment (F(7,55)=2.255 p=0.043) on water intake, as well as a significant time by treatment interaction (F(91,715)=1.541 p=0.002). All treatment groups between 0.5 and 10 mg/kg ILOP differed significantly from VEH across the treatment period (data not shown). No significant effect of time, but a significant effect of treatment (F(7,57)=2.191 p=0.048) was observed on body weight, as well as a significant time by treatment interaction (F(42,342)=4.031 p=0.000). ILOP doses between 2.5 and 20 mg/kg differed significantly for body weight from VEH, possibly due to the reductions in alcohol drinking (correlation between alcohol intake and body-weight on day 14: Pearson R= 0.64; p=0.03; data not shown). Lastly, food intake showed a significant effect of time (F(6,342)=17.671 p=0.043), no effect of group and a significant time by treatment interaction (F(42,342)=1.567 p=0.017; data not shown).

Experiment 2: ILOP reduces alcohol drinking to a similar extent as clozapine, but haloperidol does not alter alcohol drinking

When the ability of ILOP to reduce alcohol intake was compared to CLOZ and HAL, no effect of time, a significant effect of treatment (F(7,50)=9.451 p=0.000) and a significant time by treatment interaction (F(91,650)=2.467 p=0.000) were observed (Figures 2A, 2C). Only ILOP and CLOZ showed an ability to reduce alcohol drinking. Post-hoc pair-wise analyses showed that the 1, 2.5 and 5 mg/kg doses of ILOP and the 4 and 8 mg/kg doses of CLOZ treated animals drank significantly lower amounts of alcohol compared to animals treated with VEH (p=0.000) and both doses of HAL (P<0.005). None of the ILOP doses tested differed significantly from 4 mg/kg CLOZ, whereas the 8 mg/kg dose of CLOZ only differed significantly from the 1 mg/kg ILOP dose, suggesting similar reductions in alcohol intake across ILOP and CLOZ treated animals. HAL treatment did not significantly reduce alcohol drinking. Within-day between group post-hoc analysis showed that the 2.5 and 5 mg/kg ILOP and the 4 and 8 mg/kg CLOZ groups differed from VEH on days 11, 12, 13 and 14.

Figure 2. Iloperidone and clozapine reduce alcohol drinking to a similar extent, while haloperidol does not.

Figure 2

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ILOP (1-5 mg/kg) and CLOZ (4-8 mg/kg), but not HAL, reduce (A) alcohol intake and (B) alcohol preference in the hamster (mean across all days in baseline or treatment periods ± SEM; * p<0.05 compared to VEH from pair-wise analyses). (C) and (D) represent daily alcohol intake and preference respectively (daily group means ± SEM).

When the ability of ILOP to reduce alcohol preference was compared to CLOZ and HAL, a significant effect of time (F(13,650)=2.234 p=0.007), a significant effect of treatment (F(7,50)=5.677 p=0.000) and a significant time by treatment interaction (F(91,650)=2.467 p=0.000) were observed (Figure 2B, 2D). Post-hoc pair-wise analyses showed that the 2.5 mg/kg ILOP and the 4 and 8 mg/kg CLOZ treated animals drank significantly lower amounts of alcohol compared to animals treated with VEH (P=0.000) and both doses of HAL (P<0.005); the 5 mg/kg ILOP dose trended toward being significantly different from VEH (P=0.06) and from 0.2 mg/kg HAL (p=0.09). The 2.5 mg/kg ILOP dose did not differ significantly from 4 or 8 mg/kg CLOZ, whereas both 1 and 5 mg/kg ILOP differed significantly from both doses of CLOZ. HAL treatment did not significantly reduce alcohol preference.

There was a significant effect of time (F(13,663)=4.855 p=0.000) and treatment (F(7,51)=7.030 p=0.000) on water intake, but no significant time by treatment interaction. There were significant differences in water intake between 2.5 mg/kg ILOP and 4 and 8 mg/kg CLOZ (compensatory increases in water intake due to reductions in alcohol drinking) compared to VEH. Body weight showed a significant effect of time (F(6,318)=3.168 p=0.005), a significant effect of group (F(7,53)=9.376 p=0.000) and a significant time by treatment interaction (F(42, 318)=5.280 p=0.000). Animals given ILOP and CLOZ (all doses) had significantly reduced body weights compared to those given VEH. Food intake showed a significant effect of time (F(6,318)=2.704 p=0.014), a significant effect of group (F(7,53)=2.346 p=0.037) and no time by treatment interaction. The food intakes in the 4 and 8 mg/kg CLOZ groups differed significantly from VEH.

Experiment 3: Desipramine improves the ability of ILOP to decrease alcohol drinking in the hamster

We assessed the effects of ILOP, in combination with the NE reuptake inhibitor DMI, on alcohol intake. Overall, significant effects of time (F(13,728)=2.212 p=0.008) and treatment (F(8,56)=8.738 p=0.000) and a significant time by treatment interaction (F(104,728)=1.594 p=0.000) were observed (Figures 3A, 3C). Pair-wise analysis showed ILOP alone, but not DMI alone, reduced alcohol drinking, and the addition of DMI seemed to enhance this effect. As seen in earlier experiments, post-hoc overall pairwise comparisons showed that the 1 and 5 mg/kg doses of ILOP alone differed significantly from VEH (Fig. 3A); all other groups also differed significantly from VEH (p<0.005). Moreover, the combination of 1 mg/kg ILOP and 3 mg/kg DMI differed significantly from 1 mg/kg of ILOP alone (p=0.048). When 3 mg/kg of DMI was added to 5 mg/kg of ILOP, this combination differed significantly from 5 mg/kg ILOP alone (p=0.014) as well as from 3 mg/kg DMI alone (p=0.032). Within-day between group post-hoc analysis showed that the 1 and 5 mg/kg doses of ILOP combined with 3 mg/kg DMI differed from VEH on days 4, 6-8, and 10-14 (p<0.05). The 5 mg/kg ILOP plus 3mg/kg DMI group differed from 3 mg/kg DMI alone on day 11, whereas the 1 mg/kg ILOP plus 3 mg/kg DMI group differed from 1 mg/kg ILOP alone on day 11. Moreover 1 mg/kg ILOP plus 1 mg/kg DMI differed from VEH on days 7, 10-14 whereas 5 mg/kg ILOP plus 1 mg/kg DMI differed from VEH on days 6-14 (p<0.05). 1 mg/kg ILOP differed from VEH on day 12, 13 whereas 5 mg/kg DMI differed from VEH on day 14 (p<0.05). Lastly 3 mg/kg DMI also differed from VEH on days 6, 7 and 12 and 1 mg/kg DMI differed from VEH on days 7, 8 and 12 (p<0.05).

Figure 3. Desipramine improves the ability of iloperidone to decrease alcohol drinking in the hamster.

Figure 3

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DMI (3 mg/kg) improved ILOP's (1 and 5 mg/kg) ability to reduce (A) alcohol intake and (B) alcohol preference in the hamster (mean across all days in baseline or treatment periods ± SEM; * p<0.05 compared to VEH from pair-wise analyses). (C) and (D) represent daily alcohol intake and preference respectively (daily group means ± SEM).

Alcohol preference showed significant effects of time (F(13,728)=2.851 p=0.001) and treatment (F(8,56)=6.439 p=0.000) and a significant time by treatment interaction (F(104,728)=2.489 p=0.000) was observed (Figures 3B, 3D). As with alcohol intake, post-hoc overall pairwise comparisons showed that all groups also differed significantly from VEH (p<0.005). Moreover, the combination of 1 mg/kg ILOP and 3 mg/kg DMI differed significantly from 1 mg/kg ILOP alone (p=0.020). Within-day between group post-hoc analysis showed that 5 mg/kg ILOP combined with 3 mg/kg DMI differed from VEH on days 11 and 12, whereas the combination of 1 mg/kg ILOP and 3 mg/kg DMI differed from VEH on day 12. Moreover 5 mg/kg ILOP plus 1 mg/kg DMI differed from VEH on days 10, 11 and 14 (p<0.05).

There was a significant effect of time (F(13,728)=30.008 p=0.000) and treatment (F(8,56)=3.152 p=0.005) on water intake, and significant time by treatment interaction (F(104,728)=1.872 p=0.000). There were significant differences in water intake between all groups compared to VEH-treated animals (compensatory increases in water intake due to reductions in alcohol drinking). Body weight showed a significant effect of time (F(6,348)=2.147 p=0.048), a significant effect of group (F(8,58)=7.465 p=0.000) and a significant time by treatment interaction (F(48, 348)=4.396 p=0.000). All drug groups had lower body-weights compared to VEH, possibly due to reduced alcohol intake. The 1 mg/kg ILOP plus 3 mg/kg DMI and 5 mg/kg ILOP plus 1 m/kg DMI groups also differed significantly from their respective DMI alone groups for body-weight. Food intake showed a significant effect of time (F(6,348)=2.578 p=0.019), no effect of group (F(7,53)=2.346 p=0.037) and a significant time by treatment interaction (F(48, 348)=1.509 p=0.021).

Experiment 4: Idazoxan (IDAZ) does not improve ILOP's ability to reduce alcohol intake

We assessed the effects of ILOP, in combination with the NE alpha-2 receptor antagonist IDAZ, on alcohol intake (Figures 4A, 4C). Overall, a significant effect of time (F(13,793)=2.353, p=0.004) and treatment (F(9,61)=8.459, p=0.002) and a significant time by treatment interaction (F(117,793)=2.310, p=0.000) were observed on alcohol intake. Pairwise analyses showed that animals receiving ILOP alone (1 mg/kg or 5 mg/kg) or in combination with IDAZ (1.5 or 3 mg/kg) drank significantly less alcohol when compared to VEH (p<0.05). The combination groups, however, did not differ from the ILOP alone groups -- suggesting no additional impact of IDAZ on alcohol intake. Within-day between group analysis showed that the 1 mg/kg ILOP combined with either doses of IDAZ differed significantly from VEH on days 10-14. 5 mg/kg ILOP combined with 1.5 mg/kg IDAZ also differed from VEH on days 10 and 12-14 while the higher dose IDAZ with 5 mg/kg ILOP differed on days 12-14. 1 mg/kg ILOP differed from VEH on days 10-14, whereas 5 mg/kg ILOP differed from VEH on days 12-14. No drug combinations differed from the respective ILOP doses alone.

Figure 4. Idazoxan does not improve iloperidone's ability to reduce alcohol intake.

Figure 4

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IDAZ (1.5 or 3 mg/kg) did not increase ILOP's (1 and 5 mg/kg) ability to reduce (A) alcohol intake and (B) alcohol preference in the hamster (mean across all days in baseline or treatment periods ± SEM; * p<0.05 compared to VEH from pair-wise analyses). (C) and (D) represent daily alcohol intake and preference respectively (daily group means ± SEM).

For alcohol preference a significant effect of time (F(13,793)=7.928, p=0.000) and treatment (F(9,61)=3.914, p=0.001) and a significant time by treatment interaction (F(117,793)=2.278, p=0.000) were observed (Figures 4B, 4D). Pair-wise analyses showed that animals receiving ILOP alone (1 mg/kg or 5 mg/kg) or in combination with IDAZ (1.5 or 3 mg/kg) showed much less alcohol preference when compared to VEH (p<0.05). The combination groups, however, did not differ from the ILOP alone groups -- suggesting no additional impact of IDAZ on alcohol intake. Within-day between group analysis showed that the 5 mg/kg ILOP combined with either doses of IDAZ differed significantly from VEH on day 14. 1 mg/kg ILOP alone as 1 mg/kg ILOP plus both doses of IDAZ trended toward being different from VEH on day 14 (p<0.07).

There was a significant effect of time (F(13,793)=4.043 p=0.001), no effect of treatment (F(8,56)=3.152 p=0.005), and a significant time by treatment interaction (F(117,793)=1.267 p=0.038) on water intake. Body weight showed no effect of time, a significant effect of group (F(9,63)=6.995 p=0.000) and a significant time by treatment interaction (F(54,378)=6.345 p=0.000). Food intake showed a significant effect of time (F(6,378)=2.147 p=0.048), no effect of group and no time by treatment interaction). Pair-wise comparisons showed that both the ILOP doses and the 1.5 mg/kg dose of IDAZ resulted in significantly lower body-weight compared to VEH.

Discussion

In this study, we showed that ILOP, an atypical antipsychotic with a ratio of alpha-2 receptor/D2 receptor blockade similar to CLOZ, significantly reduced alcohol drinking in the Syrian golden hamster to the same extent as CLOZ. Furthermore, ILOP's ability to reduce alcohol drinking could be enhanced by the co-administration of DMI, but not IDAZ. These findings are consistent with our neurobiologic formulation regarding the actions of CLOZ toward reducing alcohol drinking in patients with SCZ -- that a weak DA D2 blockade (achieved via low doses of ILOP) combined with NE alpha-2 antagonism and NE reuptake inhibition contribute to CLOZ's ability to reduce alcohol drinking (Green et al., 1999; Khokhar et al., 2015). This study also presents the most promising agent to date for reconstructing a CLOZ-like drug, since ILOP alone was able to reduce alcohol drinking to the same extent as CLOZ.

ILOP, in addition to having a similar alpha-2/DA D2 antagonism ratio, also has similar behavioral and neurochemical effects to CLOZ. ILOP substitutes completely for CLOZ in a discriminative stimulus paradigm in C57Bl/6 mice (Philibin et al., 2009), and both CLOZ and ILOP increase social interaction between a pair of unfamiliar rats (Corbett et al., 1993). Another study assessing the effects of various antipsychotics on excitatory synaptic transmission in the prefrontal cortex showed that unlike HAL, neither CLOZ nor ILOP depressed excitatory synaptic activity in layer V prefrontal cortical neurons (Gemperle et al., 2003). The fact that the addition of DMI, but not IDAZ, enhanced the actions of ILOP suggests that the alpha-2 antagonism in ILOP is sufficiently potent to produce a CLOZ-like effect on alcohol drinking. In fact, of the four typical and atypical antipsychotics (i.e., HAL, risperidone, paliperidone and ILOP) that we have tested as potential agents to build a CLOZ-like drug upon (Gulick et al., 2014; Khokhar et al., 2015), ILOP produces the most marked reduction in alcohol drinking by itself, providing further proof for our hypothesis that the similarity in alpha-2/DA D2 receptor antagonism ratio between CLOZ and ILOP may make ILOP a likely candidate for the creation of a CLOZ-like drug for reducing alcohol use in patients with schizophrenia.

Our hypothesis regarding the importance of potent NE alpha-2, weak DA D2 antagonism and NE reuptake inhibition is further supported by pre-clinical studies that have established the potential mechanisms underlying the superiority of CLOZ. A combination of raclopride (at low doses) and IDAZ was able to enhance cortical glutamatergic transmission, and improve cognitive functioning in the MK-801-treated rat model of SCZ (Marcus et al., 2005). Moreover, in this model, the addition of IDAZ enhanced the antipsychotic effects of risperidone, facilitated dopaminergic and glutamatergic neurotransmission, and allowed a lower dose of risperidone to achieve maximal effect (Marcus et al., 2010b). Consistent with the findings here, the addition of the NE reuptake inhibitor, reboxetine, to olanzapine (another atypical antipsychotic) also enhanced olanzapine's antipsychotic effects as well as glutamatergic and dopaminergic neurotransmission (Marcus et al., 2010a). Since CLOZ can also directly modulate glutamatergic circuitry (Heresco-Levy, 2003), we will explore the potential role of these mechanisms in mediating CLOZ's effects on alcohol drinking future studies, as well as the potential combination of ILOP with glutamatergic agents to achieve a CLOZ-like effect.

The doses of ILOP used in this study are similar to those that have been shown to improve schizophrenia-like symptoms in rodent models. Doses between 1 and 3 mg/kg of ILOP reduce the ability of apomorphine and phencyclidine to disrupt pre-pulse inhibition in rats (Barr et al., 2006). The human equivalent dose range (Reagan-Shaw et al., 2008) for 1 to 3 mg/kg (0.14 to 0.40 mg/kg/day) in rodents is consistent with what is used in the clinic (6-12 mg given twice per day). This would suggest that at doses used in patients to manage psychotic symptoms with schizophrenia, ILOP treatment may also be able to reduce alcohol drinking, thus decreasing the morbidity associated with AUD in SCZ.

Furthermore, since ILOP has a more favorable side-effect profile than CLOZ (e.g., no risk of agranulocytosis, modest weight gain and no medically important changes in lipid, glucose or prolactin levels (Citrome et al., 2015), it may be more likely to be used in patients. The human equivalent dose of DMI (Reagan-Shaw et al., 2008) used here (8-24 mg/day) is considerably lower than the doses used in depressed patients clinically (100-200 mg/day), thereby reducing the possibility of adverse effects from the addition of DMI in patients with schizophrenia and AUD. Lastly, while we do not expect ILOP to alter the metabolism of alcohol due to a lack of interaction with alcohol metabolizing enzymes, desipramine has conclusively been found to not alter the metabolism or clearance of alcohol (Monostory et al., 2004; Simon O'Brien et al., 2011).

In summary, the current data from this study confirms our hypothesis that CLOZ's efficacy toward reducing alcohol drinking may depend, at least in part, upon its alpha-2/DA D2 receptor antagonism ratio and its norepinephrine reuptake inhibition. Our study further suggests that using our neurobiologic formulation of the actions of CLOZ, we were able to identify a novel antipsychotic, ILOP, which may serve as a foundation to build a safer CLOZ-like drug (Green et al., 1999). On the basis of our data, we suggest that patients with schizophrenia with co-occurring alcohol use disorder should be tested with ILOP (and potentially in combination with low doses of DMI) to assess whether ILOP alone or the combination with DMI will both manage psychotic symptoms and decrease alcohol drinking.

HIGHLIGHTS.

  • Iloperidone alone reduces alcohol drinking in the Syrian golden hamster

  • Iloperidone and clozapine reduce alcohol drinking to a similar extent

  • Desipramine enhances iloperidone's ability to reduce alcohol drinking

Acknowledgements

This work was supported in part by grants from the National Institute of Alcohol Abuse and Alcoholism (AIG; 1R03AA014644 and 1R01AA018151-02), from the National Center for Advancing Translational Science (AIG; NCATS UL1TR001086) and by an investigator-initiated research grant from Novartis Pharmaceuticals.

Footnotes

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