Yohimbine as a pharmacological probe for alcohol research: a systematic review of rodent and human studies

Cebranopadol, a novel long-acting opioid agonist with low abuse liability, to treat opioid use disorder: Preclinical evidence of efficacy

Maintenance therapy with buprenorphine and methadone is the gold standard pharmacological treatment for opioid use disorder (OUD). Despite these compounds demonstrating substantial efficacy, a significant number of patients do not show optimal therapeutic responses. The abuse liability of these medications is also a concern. Here we used rats to explore the therapeutic potential of the new long-acting pan-opioid agonist Cebranopadol in OUD. We tested the effect of cebranopadol on heroin self-administration and yohimbine-induced reinstatement of heroin seeking. In addition, we evaluated the abuse liability potential of cebranopadol in comparison to that of heroin under fixed ratio 1 (FR1) and progressive ratio (PR) operant self-administration contingencies. Oral administration of cebranopadol (0, 25, 50 μg/kg) significantly attenuated drug self-administration independent of heroin dose (1, 7, 20, 60μg/inf). Cebranopadol also reduced the break point for heroin (20 μg/inf). Finally, pretreatment with cebranopadol significantly attenuated yohimbine-induced reinstatement of drug seeking. In abuse liability experiments under FR1 contingency, rats maintained responding for heroin (1, 7, 20, 60μg/inf) to a larger extent than cebranopadol (0.03, 0.1, 0.3, 1.0, 6.0μg/inf). Under PR contingency, heroin maintained responding at high levels at all except the lowest dose, while the break point (BP) for cebranopadol did not differ from that of saline. Together, these data indicate that cebranopadol is highly efficacious in attenuating opioid self-administration and stress-induced reinstatement, while having limited abuse liability properties. Overall, the data suggest clinical potential of this compound for OUD treatment.

The anxiogenic drug yohimbine is a reinforcer in male and female rats

The indole alkaloid yohimbine is an anxiogenic drug that activates stress-responsive systems in the brain. However, because yohimbine also elicits approach behaviors, this study employed male and female Sprague-Dawley rats to explore its potential reinforcing effects. Thus, it was first determined if intravenous (IV) infusions of yohimbine (0.25 mg/kg/infusion) could maintain lever pressing, whether intake could be modulated by dose/infusion, and if lever pressing would persist in the absence of yohimbine or yohimbine-paired cues. Next, to assess yohimbine's effect on memory consolidation, 0.3, 1.25 or 3 mg/kg yohimbine was administered post-training using an object recognition memory task. Finally, place conditioning assessed whether doses of yohimbine that elevate blood serum corticosterone levels (1.25 or 3 mg/kg) could elicit a conditioned place preference. It was found that both sexes acquired yohimbine IV self-administration, that intake was modulated by dose/infusion, and that lever pressing persisted during extinction and in the absence of the yohimbine-paired cue. As well, post-training injections of 1.25 mg/kg yohimbine enhanced consolidation of object memory, and 1.25 and 3 mg/kg elevated corticosterone levels and elicited a place preference in both sexes. Finally, in behavioral tests of psychomotor functions, acute yohimbine increased lever pressing for a visual cue and elevated locomotor activity. These findings reveal a profile of yohimbine's behavioral effects that is consistent with that of psychostimulant reinforcing drugs.

Early social isolation differentially affects the glucocorticoid receptor system and alcohol-seeking behavior in male and female Marchigian Sardinian alcohol-preferring rats

Adverse early life experiences during postnatal development can evoke long-lasting neurobiological changes in stress systems, thereby affecting subsequent behaviors including propensity to develop alcohol use disorder. Here, we exposed genetically selected male and female Marchigian Sardinian alcohol-preferring (msP) and Wistar rats to mild, repeated social deprivation from postnatal day 14 (PND14) to PND21 and investigated the effect of the early social isolation (ESI) on the glucocorticoid receptor (GR) system and on the propensity to drink and seek alcohol in adulthood. We found that ESI resulted in higher levels of GR gene and protein expression in the prefrontal cortex (PFC) in male but not female msP rats. In female Wistars, ESI resulted in significant downregulation of Nr3c1 mRNA levels and lower GR protein levels. In male and female msP rats, plasma corticosterone levels on PND35 were similar and unaffected by ESI. Wistar females exhibited higher levels of corticosterone compared with males, independently from ESI. In alcohol self-administration experiments we found that the pharmacological stressor yohimbine (0.0, 0.312, 0.625, and 1.25 mg/kg) increased alcohol self-administration in both rat lines, regardless of ESI. After extinction, 0.625 mg/kg yohimbine significantly reinstated alcohol seeking in female rats only. ESI enhanced reinstatement in female msP rats. Overall, the present results indicate that repeated social deprivation during the third week of postnatal life affects GR expression in a strain- and sex-dependent manner: such effect may contribute, at least partially, to the heightened sensitivity of female msP rats to the effects of yohimbine-induced alcohol seeking.

The Rauvolfia tetraphylla genome suggests multiple distinct biosynthetic routes for yohimbane monoterpene indole alkaloids

Monoterpene indole alkaloids (MIAs) are a structurally diverse family of specialized metabolites mainly produced in Gentianales to cope with environmental challenges. Due to their pharmacological properties, the biosynthetic modalities of several MIA types have been elucidated but not that of the yohimbanes. Here, we combine metabolomics, proteomics, transcriptomics and genome sequencing of Rauvolfia tetraphylla with machine learning to discover the unexpected multiple actors of this natural product synthesis. We identify a medium chain dehydrogenase/reductase (MDR) that produces a mixture of four diastereomers of yohimbanes including the well-known yohimbine and rauwolscine. In addition to this multifunctional yohimbane synthase (YOS), an MDR synthesizing mainly heteroyohimbanes and the short chain dehydrogenase vitrosamine synthase also display a yohimbane synthase side activity. Lastly, we establish that the combination of geissoschizine synthase with at least three other MDRs also produces a yohimbane mixture thus shedding light on the complex mechanisms evolved for the synthesis of these plant bioactives.

Cebranopadol, a novel long-acting opioid agonist with low abuse liability, to treat opioid use disorder: Preclinical evidence of efficacy

The gold standard pharmacological treatment for opioid use disorder (OUD) consists of maintenance therapy with long-acting opioid agonists such as buprenorphine and methadone. Despite these compounds having demonstrated substantial efficacy, a significant number of patients do not show optimal therapeutic responses. Moreover, the abuse liability of these medications remains a major concern. Cebranopadol, is a new, long-acting pan-opioid agonist that also activates the nociception/orphanin FQ NOP receptor. Here we used rats to explore the therapeutic potential of this agent in OUD. First, in operant intravenous self-administration experiments we compared the potential abuse liability of cebranopadol with the prototypical opioid heroin. Under a fixed ratio 1 (FR1) contingency, rats maintained responding for heroin (1, 7, 20, 60 μg/inf) to a larger extent than cebranopadol (0.03, 0.1, 0.3, 1.0, 6.0 μg/inf). When the contingency was switched to a progressive ratio (PR) reinforcement schedule, heroin maintained responding at high levels at all except the lowest dose. Conversely, in the cebranopadol groups responding decreased drastically and the break point (BP) did not differ from saline controls. Next, we demonstrated that oral administration of cebranopadol (0, 25, 50 μg/kg) significantly attenuated drug self-administration independent of heroin dose (1, 7, 20, 60 μg/inf). Cebranopadol also reduced the break point for heroin (20 μg/inf). Furthermore, in a heroin self-administration training extinction/reinstatement paradigm, pretreatment with cebranopadol significantly attenuated yohimbine stress-induced reinstatement of drug seeking. Together, these data indicate that cebranopadol has limited abuse liability compared to heroin and is highly efficacious in attenuating opioid self-administration and stress-induced reinstatement, suggesting clinical potential of this compound for OUD treatment.

Mifepristone as a pharmacological intervention for stress-Induced alcohol craving: a translational crossover randomized trial

Preclinical and clinical work suggests that mifepristone (glucocorticoid receptor antagonist), may be a viable treatment for alcohol use disorder (AUD). The aim of this work was to translate our preclinical mifepristone study using yohimbine (α2 receptor antagonist) stress-induced reinstatement of alcohol-seeking to a clinical setting. This was a Phase 1/2, outpatient, cross-over, randomized, double-blind, placebo-controlled trial with non-treatment-seeking individuals with AUD ( N =32). We investigated the safety, alcohol craving and consumption after oral administration of mifepristone (600mg daily for a week) in a human laboratory study comprised of administration of yohimbine in a cue-reactivity procedure and alcohol self-administration. Outcomes were assessed using Generalized Estimating Equations and mediation and moderation analyses assessed mechanisms of action and precision medicine targets. We did not observe serious adverse events related to the study drugs or study procedure and mild to moderate non-serious adverse events were reported by both study conditions. Also, there was no statistically-significant difference between the mifepristone and placebo in the hemodynamic response, alcohol subjective effects and pharmacokinetics parameters. Mifepristone significantly reduced alcohol craving and increased cortisol levels. Mifepristone-induced cortisol increase was not a mediator of alcohol craving. Moderation analysis with family history density of AUD (FHDA) and mifepristone, suggested that reduced craving was present in individuals with low , but not high FHDA. Mifepristone, compared to placebo, did not reduce alcohol consumption in the laboratory or in a naturalistic setting. This study successfully translated a preclinical paradigm to a human laboratory study confirming safety, tolerability and efficacy of mifepristone in an alcohol paradigm. Mediation analysis showed that the effect of mifepristone on craving was not related to mifepristone-induced increases in cortisol and moderation of FHDA suggested the importance of evaluating AUD endophenotypes for pharmacotherapies.

Clinical trial registration

Clinicaltrials.gov ; NCT02243709.

IND/FDA

121984, mifepristone and yohimbine (Holder: Haass-Koffler).