Increased locomotor activity induced by heroin in mice: pharmacokinetic demonstration of heroin acting as a prodrug for the mediator 6-monoacetylmorphine in vivo

Distribution of morphine and methadone to the brain in a developmental chicken embryo model

The use and/or misuse of opioids by pregnant women would expose the fetuses to these drugs during critical stages of development with serious effects for the newborn, like the neonatal abstinence syndrome (NAS). We have revisited an established chicken model for NAS to describe the distribution of morphine and methadone to the brain and explore its validity as a valuable alternative to rodent models. For this purpose, chicken eggs were injected with a single dose of 10 mg/kg or 20 mg/kg morphine or 20 mg/kg methadone onto the chorioallantoic membrane (CAM) on embryonal day 13. Whole brains and lungs were harvested and the concentrations of morphine, methadone and their subsequent metabolites (morphine-3-glucuronide and EDDP, respectively) determined in the brain and lungs at different time points using LC-MS/MS. Morphine and methadone, as well as their metabolites, were detected both in the brain and lungs, with significantly higher concentrations in the lungs. Pharmacokinetic modelling showed that the distribution of morphine to the brain followed a first-order absorption with transit compartments and linear elimination, with concentrations linearly dependent on dose. Moreover, methadone, but not morphine, reduced μ receptor (the main morphine receptor) binding, which can be of relevance for opioid tolerance. The present study is the first to report the brain distribution of morphine, which can be described by standard pharmacokinetic processes, and methadone in the developing chicken embryo. The present findings supplement the already established model and support the use of this chicken model to study NAS.

Heroin metabolism in human blood and its impact for the design of an immunotherapeutic approach against heroin effects

Immunotherapeutic interventions that block drug effects by binding drug molecules to specific antibodies in the bloodstream have shown promising effects in animal studies. For heroin, which effects are mainly mediated by the metabolites 6-acetylmorphine (6-AM; also known as 6-monoacetylmorphine or 6-MAM) and morphine, the optimal antibody specificity has been discussed. In rodents, 6-AM specific antibodies have been recommended based on the rapid metabolism of heroin to 6-AM in the bloodstream. Since the metabolic rate of heroin in blood is unsettled in humans, we examined heroin metabolism with state-of-the-art analytical methodology (UHPLC-MS/MS) in freshly drawn human whole blood incubated with a wide range of heroin concentrations (1-500 μM). The half-life of heroin was highly concentration dependent, ranging from 1.2-1.7 min for concentrations at or above 25 μM, and gradually increasing to approximately 20 min for 1 μM heroin. At concentrations that can be attained in the bloodstream shortly after an i.v. injection, approximately 70% was transformed into 6-AM within 3 min, similar to previous observations in vivo. Our results indicate that blood enzymes play a more important role for the rapid metabolism of heroin in humans than previously assumed. This points to 6-AM as an important target for an efficient immunotherapeutic approach to block heroin effects in humans.

P-glycoprotein (MDR1/ABCB1) Restricts Brain Penetration of the Main Active Heroin Metabolites 6-monoacetylmorphine (6-MAM) and Morphine in Mice

BACKGROUND & PURPOSE

Heroin (diacetylmorphine; diamorphine) is a highly addictive opioid prodrug. Heroin prescription is possible in some countries for chronic, treatment-refractory opioid-dependent patients and as a potent analgesic for specific indications. We aimed to study the pharmacokinetic interactions of heroin and its main pharmacodynamically active metabolites, 6-monoacetylmorphine (6-MAM) and morphine, with the multidrug efflux transporters P-glycoprotein/ABCB1 and BCRP/ABCG2 using wild-type, Abcb1a/1b and Abcb1a/1b;Abcg2 knockout mice.

METHODS & RESULTS

Upon subcutaneous (s.c.) heroin administration, its blood levels decreased quickly, making it challenging to detect heroin even shortly after dosing. 6-MAM was the predominant active metabolite present in blood and most tissues. At 10 and 30 min after heroin administration, 6-MAM and morphine brain accumulation were increased about 2-fold when mouse (m)Abcb1a/1b and mAbcg2 were ablated. Fifteen minutes after direct s.c. administration of an equimolar dose of 6-MAM, we observed good intrinsic brain penetration of 6-MAM in wild-type mice. Still, mAbcb1 limited brain accumulation of 6-MAM and morphine without affecting their blood exposure, and possibly mediated their direct intestinal excretion. A minor contribution of mAbcg2 to these effects could not be excluded.

CONCLUSIONS

We show that mAbcb1a/1b can limit 6-MAM and morphine brain exposure. Pharmacodynamic behavioral/postural observations, while non-quantitative, supported moderately increased brain levels of 6-MAM and morphine in the knockout mouse strains. Variation in ABCB1 activity due to genetic polymorphisms or environmental factors (e.g., drug interactions) might affect 6-MAM/morphine exposure in individuals, but only to a limited extent.

Heroin and its metabolites: relevance to heroin use disorder

Heroin is an opioid agonist commonly abused for its rewarding effects. Since its synthesis at the end of the nineteenth century, its popularity as a recreational drug has ebbed and flowed. In the last three decades, heroin use has increased again, and yet the pharmacology of heroin is still poorly understood. After entering the body, heroin is rapidly deacetylated to 6-monoacetylmorphine (6-MAM), which is then deacetylated to morphine. Thus, drug addiction literature has long settled on the notion that heroin is little more than a pro-drug. In contrast to these former views, we will argue for a more complex interplay among heroin and its active metabolites: 6-MAM, morphine, and morphine-6-glucuronide (M6G). In particular, we propose that the complex temporal pattern of heroin effects results from the sequential, only partially overlapping, actions not only of 6-MAM, morphine, and M6G, but also of heroin per se, which, therefore, should not be seen as a mere brain-delivery system for its active metabolites. We will first review the literature concerning the pharmacokinetics and pharmacodynamics of heroin and its metabolites, then examine their neural and behavioral effects, and finally discuss the possible implications of these data for a better understanding of opioid reward and heroin addiction. By so doing we hope to highlight research topics to be investigated by future clinical and pre-clinical studies.

Increased heroin intake and relapse vulnerability in intermittent relative to continuous self-administration: Sex differences in rats

BACKGROUND AND PURPOSE

Studies using intermittent-access drug self-administration show increased motivation to take and seek cocaine and fentanyl, relative to continuous access. In this study, we examined the effects of intermittent- and continuous-access self-administration on heroin intake, patterns of self-administration and cue-induced heroin-seeking, after forced or voluntary abstinence, in male and female rats. We also modelled brain levels of heroin and its active metabolites.

EXPERIMENTAL APPROACH

Rats were trained to self-administer a palatable solution and then heroin (0.075 mg·kg^-1 per inf) either continuously (6 h·day^-1 ; 10 days) or intermittently (6 h·day^-1 ; 5-min access every 30-min; 10 days). Brain levels of heroin and its metabolites were modelled using a pharmacokinetic software. Next, heroin-seeking was assessed after 1 or 21 abstinence days. Between tests, rats underwent either forced or voluntary abstinence. The oestrous cycle was measured using a vaginal smear test.

KEY RESULTS

Intermittent access exacerbated heroin self-administration and was characterized by a burst-like intake, yielding higher brain peaks of heroin and 6-monoacetylmorphine concentrations. Moreover, intermittent access increased cue-induced heroin-seeking during early, but not late abstinence. Heroin-seeking was higher in females after intermittent, but not continuous access, and this effect was independent of the oestrous cycle.

CONCLUSIONS AND IMPLICATIONS

Intermittent heroin access in rats resembles critical features of heroin use disorder: a self-administration pattern characterized by repeated large doses of heroin and higher relapse vulnerability during early abstinence. This has significant implications for refining animal models of substance use disorder and for better understanding of the neuroadaptations responsible for this disorder.

LINKED ARTICLES

This article is part of a themed issue on Advances in Opioid Pharmacology at the Time of the Opioid Epidemic. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v180.7/issuetoc.

Prenatal heroin exposure alters brain morphology and connectivity in adolescent mice

The United States is experiencing a dramatic increase in maternal opioid misuse and, consequently, the number of individuals exposed to opioids in utero. Prenatal opioid exposure has both acute and long-lasting effects on health and wellbeing. Effects on the brain, often identified at school age, manifest as cognitive impairment, attention deficit, and reduced scholastic achievement. The neurobiological basis for these effects is poorly understood. Here, we examine how in utero exposure to heroin affects brain development into early adolescence in a mouse model. Pregnant C57BL/6J mice received escalating doses of heroin twice daily on gestational days 4-18. The brains of offspring were assessed on postnatal day 28 using 9.4 T diffusion MRI of postmortem specimens at 36 μm resolution. Whole-brain volumes and the volumes of 166 bilateral regions were compared between heroin-exposed and control offspring. We identified a reduction in whole-brain volume in heroin-exposed offspring and heroin-associated volume changes in 29 regions after standardizing for whole-brain volume. Regions with bilaterally reduced standardized volumes in heroin-exposed offspring relative to controls include the ectorhinal and insular cortices. Regions with bilaterally increased standardized volumes in heroin-exposed offspring relative to controls include the periaqueductal gray, septal region, striatum, and hypothalamus. Leveraging microscopic resolution diffusion tensor imaging and precise regional parcellation, we generated whole-brain structural MRI diffusion connectomes. Using a dimension reduction approach with multivariate analysis of variance to assess group differences in the connectome, we found that in utero heroin exposure altered structure-based connectivity of the left septal region and the region that acts as a hub for limbic regulatory actions. Consistent with clinical evidence, our findings suggest that prenatal opioid exposure may have effects on brain morphology, connectivity, and, consequently, function that persist into adolescence. This work expands our understanding of the risks associated with opioid misuse during pregnancy and identifies biomarkers that may facilitate diagnosis and treatment.

Development of an Effective Monoclonal Antibody against Heroin and Its Metabolites Reveals Therapies Have Mistargeted 6-Monoacetylmorphine and Morphine over Heroin

The opioid epidemic is a global public health crisis that has failed to abate with current pharmaceutical treatments. Moreover, these FDA-approved drugs possess numerous problems such as adverse side effects, short half-lives, abuse potential, and recidivism after discontinued use. An alternative treatment model for opioid use disorders is immunopharmacotherapy, where antibodies are produced to inhibit illicit substances by sequestering the drug in the periphery. Immunopharmacotherapeutics against heroin have engaged both active and passive vaccines targeting heroin's metabolites, 6-monoacetylmorphine (6-AM) and morphine, since decades of research have stated that heroin's psychoactive and lethal effects are mainly attributed to these compounds. However, concerted efforts to develop effective immunopharmacotherapies against heroin abuse have faced little clinical advancement, suggesting a need for reassessing drug target selection. To address this issue, four unique monoclonal antibodies were procured with distinct affinity to either heroin, 6-AM, or morphine. Examination of these antibodies through in vitro and in vivo tests revealed monoclonal antibody 11D12 as the optimal therapeutic and provided crucial insights into the key chemical species to target for blunting heroin's psychoactive and lethal effects. These findings offer clarification into the problematic attempts of therapeutics targeting heroin's metabolites and provide a path forward for future heroin immunopharmacotherapy development.

Morphine Accumulates in the Retina Following Chronic Systemic Administration

Opioid transport into the central nervous system is crucial for the analgesic efficacy of opioid drugs. Thus, the pharmacokinetics of opioid analgesics such as morphine have been extensively studied in systemic circulation and the brain. While opioid metabolites are routinely detected in the vitreous fluid of the eye during postmortem toxicological analyses, the pharmacokinetics of morphine within the retina of the eye remains largely unexplored. In this study, we measured morphine in mouse retina following systemic exposure. We showed that morphine deposits and persists in the retina long after levels have dropped in the serum. Moreover, we found that morphine concentrations (ng/mg tissue) in the retina exceeded brain morphine concentrations at all time points tested. Perhaps most intriguingly, these data indicate that following chronic systemic exposure, morphine accumulates in the retina, but not in the brain or serum. These results suggest that morphine can accumulate in the retina following chronic use, which could contribute to the deleterious effects of chronic opioid use on both image-forming and non-image-forming visual functions.

Physiological dependence to mitragynine indicated by a rapid cross-dependence procedure with heroin-dependent mice

The potential of mitragynine to produce physiological dependence (withdrawal) was assessed using a rapid assessment procedure with male ICR mice exposed to heroin-admixed food followed by naloxone (subcutaneously, s.c.) precipitation of withdrawal. Initial studies indicated that 3 days of exposure to 3.0 mg/g of heroin-admixed food followed by naloxone (0.6 mg/kg) reliably precipitated withdrawal jumping and weight loss. Lower concentrations of heroin-admixed food and lower doses of naloxone produced fewer withdrawal signs. A longer exposure to heroin-admixed food did not produce significantly greater amounts of jumping or weight loss. Further, these withdrawal signs were dose-dependently reversed by s.c. administration of heroin immediately following naloxone administration. Mitragynine (s.c.) also dose-dependently suppressed naloxone-precipitated withdrawal signs. Additionally, both jumping and weight loss were suppressed over a comparable range of mitragynine doses when administered by gavage with a noticeably, but not significantly, higher potency than with s.c. administration. The ED₅₀ values for mitragynine for the suppression of withdrawal by any route (354-911 μmol/kg) were greater than the minimally effective dose that decreased locomotor activity (251 μmol/kg) and from 40- to 104-fold greater than those for heroin. The results suggest inherent opioid dependence liability of mitragynine. The in vivo potency relations between mitragynine and heroin are consistent with a conclusion of dependence-producing effects, indicated by the suppression of withdrawal, comparable to standard opioid μ-receptor agonists, differing primarily in terms of potency. The present paper provides a method for the rapid assessment of physiological dependence liability applicable to other kratom plant constituents or any potential opioid dependence-producing agents.

Cingulate circuits are associated with escalation of heroin use and naloxone-induced increases in heroin self-administration

Opioid use disorder (OUD) is defined as a compulsion to seek and take opioids, loss of control over intake and the development of a negative emotional state when access to opioids is denied. Using functional magnetic resonance imaging (fMRI) data in a rat model of OUD, we demonstrate that the escalation of heroin self-administration (SA) and the increased heroin SA following an injection of an opioid receptor antagonist (naloxone) are associated with changes in distinct brain circuits, centered on the cingulate cortex (Cg). Here, SA escalation score was negatively associated with changes in resting state functional connectivity (rsFC) between the Cg and the dorsal striatum. Conversely, increased heroin SA following naloxone injection, was associated with increased connectivity between the Cg and the extended amygdala and hypothalamus. Naloxone-induced increased SA was also positively associated with changes in the amplitude of low frequency fluctuations within the Cg, a measure of spontaneous neuronal activity. Characterizing the distinct brain circuit and behavior changes associated with different facets of addiction increases our understanding of OUD and may provide insight into addiction prevention and treatment.

Diamorphine for pain and distress in young patients: case examples and discussion of mechanisms

Diamorphine is a strong opioid licensed in the UK for many uses, including moderate and severe pain. In the early 2000s, its use in palliative medicine was widespread before a supply disruption led to preferential use of alternative, cheaper opioids. Though these supply issues were resolved, the use of diamorphine in palliative medicine has remained reduced, particularly with another UK supply disruption in 2021. Following anecdotal reports of good results from diamorphine use in younger patients, this piece discusses two cases of young patients with metastatic cancers suffering significant pain and psychological distress. Both patients were approaching end of life and required high doses of opioids, benzodiazepines and co-analgesics, all given to limited benefit. Both patients were rotated to diamorphine giving objective and subjective improvement in symptoms. These cases are presented in the context of newer information and description of the biochemical actions of diamorphine and its metabolites, which exert their own clinical effect before themselves generating active metabolites. Various trials on, and discussion about, diamorphine's unique metabolism and subsequent central nervous system effects help argue for its use in situations where extreme pain and psychological distress overlap.

The Application of Metabolomics in Forensic Science with Focus on Forensic Toxicology and Time-of-Death Estimation

Recently, the diagnostic methods used by scientists in forensic examinations have enormously expanded. Metabolomics provides an important contribution to analytical method development. The main purpose of this review was to investigate and summarize the most recent applications of metabolomics in forensic science. The primary research method was an extensive review of available international literature in PubMed. The keywords “forensic” and “metabolomics” were used as search criteria for the PubMed database scan. Most authors emphasized the analysis of different biological sample types using chromatography methods. The presented review is a summary of recently published implementations of metabolomics in forensic science and types of biological material used and techniques applied. Possible opportunities for valuable metabolomics’ applications are discussed to emphasize the essential necessities resulting in numerous nontargeted metabolomics’ assays.

Comparative Neuropharmacology and Pharmacokinetics of Methamphetamine and Its Thiophene Analog Methiopropamine in Rodents

Methiopropamine is a novel psychoactive substance (NPS) that is associated with several cases of clinical toxicity, yet little information is available regarding its neuropharmacological properties. Here, we employed in vitro and in vivo methods to compare the pharmacokinetics and neurobiological effects of methiopropamine and its structural analog methamphetamine. Methiopropamine was rapidly distributed to the blood and brain after injection in C57BL/6 mice, with a pharmacokinetic profile similar to that of methamphetamine. Methiopropamine induced psychomotor activity, but higher doses were needed (E_max 12.5 mg/kg; i.p.) compared to methamphetamine (E_max 3.75 mg/kg; i.p.). A steep increase in locomotor activity was seen after a modest increase in the methiopropamine dose from 10 to 12.5 mg/kg, suggesting that a small increase in dosage may engender unexpectedly strong effects and heighten the risk of unintended overdose in NPS users. In vitro studies revealed that methiopropamine mediates its effects through inhibition of norepinephrine and dopamine uptake into presynaptic nerve terminals (IC₅₀ = 0.47 and 0.74 µM, respectively), while the plasmalemmal serotonin uptake and vesicular uptake are affected only at high concentrations (IC₅₀ > 25 µM). In summary, methiopropamine closely resembles methamphetamine with regard to its pharmacokinetics, pharmacodynamic effects and mechanism of action, with a potency that is approximately five times lower than that of methamphetamine.

Does the preparation for intravenous administration affect the composition of heroin injections? A controlled laboratory study

AIMS

To study whether the preparation procedure, and its acidic and heating conditions, used by heroin users to prepare heroin for intravenous administration affects the final composition of the fluid to be injected.

METHODS

Samples from different seizures of illegal heroin provided by the Norwegian police were prepared by adding water and ascorbic acid before heating under controlled conditions in the laboratory. Further, three seizures were prepared with different amounts of ascorbic or citric acid relative to their diacetylmorphine content. Pure diacetylmorphine base or salt was also submitted to the procedure applying two different heating intensities. The seizures and the final product after preparation were analysed for diacetylmorphine, 6-acetylmorphine and morphine using liquid chromatography with tandem mass spectrometry (LC-MS-MS).

RESULTS

After preparation, a decrease of 19.8% (25th and 75th percentiles = -29.2 and -15.3) in the initial diacetylmorphine content was observed. Both the 6-acetylmorphine and morphine content increased but, due to their low content in the initial product, diacetylmorphine still represented 83.9% (25th and 75th percentiles = 77.3 and 88.0) of the sum of these three opioids in the final solution. The loss of water during preparation caused an increase in the concentration of diacetylmorphine, 6-acetylmorphine and morphine, depending on the heating intensity applied. The content of these opioids was affected by the quantity and type of acid added in relation to the heroin purity and the level of diacetylmorphine dissolved being proportional to the amount of ascorbic acid, but not citric acid, in the sample with high heroin purity.

CONCLUSIONS

Preparation of heroin for intravenous injection appears to change the amount or concentration of diacetylmorphine and its active metabolites, 6-acetylmorphine and morphine in the final product, depending on heroin purity, amount and type of acid used or heating conditions. These circumstances can contribute to unintentional variations in the potency of the final injected solution, and therefore affect the outcome after injection.

Peripherally administered persistent organic pollutants distribute to the brain of developing chicken embryo in concentrations relevant for human exposure

Persistent organic pollutants (POPs) can reach the fetal brain and contribute to developmental neurotoxicity. To explore the distribution of POPs to the fetal brain, we exposed chicken embryos to a POP mixture, containing 29 different compounds with concentrations based on blood levels measured in the Scandinavian human population. The mixture was injected into the allantois at embryonic day 13 (E13), aiming at a theoretical concentration of 10 times human blood levels. POPs concentrations in the brain were measured at 0.5, 1, 2, 4, 6, 24, 48, and 72 h after administration. Twenty-seven of the individual compounds were detected during at least one of the time-points analyzed. Generally, the concentrations of most of the measured compounds were within the order of magnitude of those reported in human brain samples. Differences in the speed of distribution to the brain were observed between the per- and polyfluoroalkyl substances (PFASs), which have protein binding potential, and the lipophilic polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs) and brominated flame retardants (BFRs). Based on pharmacokinetic modeling, PFASs were best described by a one compartment model. PFASs displayed relatively slow elimination (Kel) and persisted at high levels in the brain. Lipophilic OCPs and PCBs could be fitted to a 2-compartment model. These showed high levels in the brain relative to the dose administrated as calculated by area under the curve (AUC)/Dose. Altogether, our study showed that chicken is a suitable model to explore the distribution of POPs into the developing brain at concentrations which are relevant for humans.

Synthesis and immunological effects of C14-linked 4,5-epoxymorphinan analogues as novel heroin vaccine haptens

Active immunization is being explored as a potential therapeutic to combat accidental overdose and to mitigate the abuse potential of opioids. Hapten design is one of the crucial factors that determines the efficacy of a candidate vaccine to substance abuse and remains one of the most active areas of research in vaccine development. Herein we report for the first time the synthesis of three novel opiate surrogates with the linker attachment site at C14, 1 (6,14-AmidoHap), 2 (14-AmidoMorHap), and 3 (14-AmidoHerHap) as novel heroin haptens. The compounds 1, 2, and 3 are analogues with different substituents at C6: an acetamide, a hydroxyl moiety, and an acetate, respectively. All three haptens had a phenolic hydroxyl group at C3. The haptens were conjugated to the tetanus toxoid carrier protein, adjuvanted with liposomal monophosphoryl lipid A/aluminum hydroxide and were tested in mice in terms of immunogenicity and efficacy. Immunization of mice resulted in antibody endpoint titers of >10⁵ against all the haptens. Neither of the conjugates of 1, 2, and 3 had induced antibodies with selectivity broad enough to recognize and bind heroin, 6-AM, and morphine resulting in little to no protection against the antinociceptive effects of heroin in vivo. Only the mice immunized with conjugate 3 were partially protected against heroin-induced antinociception. These results contribute to the growing body of knowledge that the linker position and the subtle structural differences in the hapten scaffold impact the selectivity of the induced antibodies. Together, these highlight the importance of rational hapten design for heroin vaccine development.

Three novel opiate surrogates with the linker at C14, 1 (6,14-AmidoHap), 2 (14-AmidoMorHap), and 3 (14-AmidoHerHap) were conjugated to tetanus toxoid (TT) and tested as heroin vaccines. The C3 and C6 moieties are crucial in antibody selectivity.

Systematic Structure-Based Virtual Screening Approach to Antibody Selection and Design of a Humanized Antibody against Multiple Addictive Opioids without Affecting Treatment Agents Naloxone and Naltrexone

Opioid drug use, especially heroin, is known as a growing national crisis in America. Heroin itself is a prodrug and is converted to the most active metabolite 6-monoacetylmorphine (6-MAM) responsible for the acute toxicity of heroin and then to a relatively less-active metabolite morphine responsible for the long-term toxicity of heroin. Monoclonal antibodies (mAbs) are recognized as a potentially promising therapeutic approach in the treatment of opioid use disorders (OUDs). Due to the intrinsic challenges of discovering an mAb against multiple ligands, here we describe a general, systematic structure-based virtual screening and design approach which has been used to identify a known anti-morphine antibody 9B1 and a humanized antibody h9B1 capable of binding to multiple addictive opioids (including 6-MAM, morphine, heroin, and hydrocodone) without significant binding with currently available OUD treatment agents naloxone, naltrexone, and buprenorphine. The humanized antibody may serve as a promising candidate for the treatment of OUDs. The experimental binding affinities reasonably correlate with the computationally predicted binding free energies. The experimental activity data strongly support the computational predictions, suggesting that the systematic structure-based virtual screening and humanization design protocol is reliable. The general, systematic structure-based virtual screening and design approach will be useful for many other antibody selection and design efforts in the future.

Investigation of the Structure-Activity Relationships of Psilocybin Analogues

The 5-HT_2A receptor is thought to be the primary target for psilocybin (4-phosphoryloxy-N,N-dimethyltryptamine) and other serotonergic hallucinogens (psychedelic drugs). Although a large amount of experimental work has been conducted to characterize the pharmacology of psilocybin and its dephosphorylated metabolite psilocin (4-hydroxy-N,N-dimethyltryptamine), there has been little systematic investigation of the structure-activity relationships (SAR) of 4-substituted tryptamine derivatives. In addition, structural analogs of psilocybin containing a 4-acetoxy group, such as 4-acetoxy-N,N-dimethyltryptamine (4-AcO-DMT), have appeared as new designer drugs, but almost nothing is known about their pharmacological effects. To address the gap of information, studies were conducted with 17 tryptamines containing a variety of symmetrical and asymmetrical N,N-dialkyl substituents and either a 4-hydroxy or 4-acetoxy group. Calcium mobilization assays were conducted to assess functional activity at human and mouse 5-HT₂ subtypes. Head-twitch response (HTR) studies were conducted in C57BL/6J mice to assess 5-HT_2A activation in vivo. All of the compounds acted as full or partial agonists at 5-HT₂ subtypes, displaying similar potencies at 5-HT_2A and 5-HT_2B receptors, but some tryptamines with bulkier N-alkyl groups had lower potency at 5-HT_2C receptors and higher 5-HT_2B receptor efficacy. In addition, O-acetylation reduced the in vitro 5-HT_2A potency of 4-hydroxy-N,N-dialkyltryptamines by about 10- to 20-fold but did not alter agonist efficacy. All of the compounds induce head twitches in mice, consistent with an LSD-like behavioral profile. In contrast to the functional data, acetylation of the 4-hydroxy group had little effect on HTR potency, suggesting that O-acetylated tryptamines may be deacetylated in vivo, acting as prodrugs. In summary, the tryptamine derivatives have psilocybin-like pharmacological properties, supporting their classification as psychedelic drugs.

Enhancement of a Heroin Vaccine through Hapten Deuteration

The United States is in the midst of an unprecedented epidemic of opioid substance use disorder, and while pharmacotherapies including opioid agonists and antagonists have shown success, they can be inadequate and frequently result in high recidivism. With these challenges facing opioid use disorder treatments immunopharmacotherapy is being explored as an alternative therapy option and is based upon antibody-opioid sequestering to block brain entry. Development of a heroin vaccine has become a major research focal point; however, producing an efficient vaccine against heroin has been particularly challenging because of the need to generate not only a potent immune response but one against heroin and its multiple psychoactive molecules. In this study, we explored the consequence of regioselective deuteration of a heroin hapten and its impact upon the immune response against heroin and its psychoactive metabolites. Deuterium (H_dAc) and cognate protium heroin (H_Ac) haptens were compared head to head in an inclusive vaccine study. Strikingly the H_dAc vaccine granted greater efficacy in blunting heroin analgesia in murine behavioral models compared to the H_Ac vaccine. Binding studies confirmed that the H_dAc vaccine elicited both greater quantities and equivalent or higher affinity antibodies toward heroin and 6-AM. Blood-brain biodistribution experiments corroborated these affinity tests. These findings suggest that regioselective hapten deuteration could be useful for the resurrection of previous drug of abuse vaccines that have met limited success in the past.

Mass Spectrometric Imaging of the Brain Demonstrates the Regional Displacement of 6-Monoacetylmorphine by Naloxone

Overdose is the main cause of mortality among heroin users. Many of these overdose-induced deaths can be prevented through the timely administration of naloxone (NLX), a nonselective mu (μ)-, kappa (κ)-, and delta (δ)-opioid receptor antagonist. NLX competitively inhibits opioid-overdose-induced respiratory depression without eliciting any narcotic effect itself. The aim of this study was to investigate the antagonistic action of NLX by comparing its distribution to that of 6-monacetylmorphine (6-MAM), heroin's major metabolite, in a rodent model using mass spectrometric imaging (MSI) in combination with liquid chromatography-tandem mass spectrometry (LC-MS/MS). Male Sprague-Dawley rats (n = 5) received heroin (10 mg kg^-1) intraperitoneally, NLX (10 mg kg^-1) intranasally, and NLX injected intranasally 5 min after heroin administration. The animals were sacrificed 15 min after dose and brain tissues were harvested. The MSI image analysis showed a region-specific distribution of 6-MAM in the brain regions including the corpus callosum, hippocampal formation, cerebral cortex, corticospinal tracts, caudate putamen, thalamus, globus pallidus, hypothalamus, and basal forebrain regions of the brain. The antagonist had a similar biodistribution throughout the brain in both groups of animals that received NLX or NLX after heroin administration. The MSI analysis demonstrated that the intensity of 6-MAM in these brain regions was reduced following NLX treatment. The decrease in 6-MAM intensity was caused by its displacement by the antagonist and its binding to these receptors in these specific brain regions, consequently enhancing the opioid elimination. These findings will contribute to the evaluation of other narcotic antagonists that might be considered for use in the treatment of drug overdose via MSI.

Effects of Cebranopadol on Cocaine-induced Hyperactivity and Cocaine Pharmacokinetics in Rats

Cebranopadol is known as a highly potent analgesic. Recent studies also demonstrated that administration of cebranopadol significantly decreased cocaine self-administration and significantly reduced cue-induced cocaine-seeking behaviors in rats. However, it was unclear whether these interesting behavioral observations are related to any potential effects of cebranopadol on cocaine pharmacokinetics or cocaine-induced hyperactivity. In principle, a promising therapeutic candidate for cocaine dependence treatment may alter the cocaine pharmacokinetics and/or attenuate cocaine-induced reward and hyperactivity and, thus, decrease cocaine self-administration and reduce cue-induced cocaine-seeking behaviors. In this study, we examined possible effects of cebranopadol on cocaine pharmacokinetics and cocaine-induced hyperactivity for the first time. According to our animal data in rats, cebranopadol did not significantly alter the pharmacokinetics of cocaine. According to our more extensive locomotor activity testing data, cebranopadol itself also dose-dependently induced hyperactivity in rats at doses higher than 50 µg/kg. Cebranopadol at a low dose of 25 µg/kg (p.o.) did not induce significant hyperactivity itself, but significantly potentiated cocaine-induced hyperactivity on Days 4 to 7 after the repeated daily dosing of the drug.

Cebranopadol reduces cocaine self-administration in male rats: Dose, treatment and safety consideration

As a novel first-in-class potent analgesic acting as an agonist of multiple opioid receptors, cebranopadol showed high efficacy and good tolerability in a broad range of preclinical models and clinical trials related to pain. In the present study, to evaluate the efficacy and safety of cebranopadol as a potential treatment of cocaine dependence, we tested the effects of cebranopadol with single and repeated doses (25, 50, 75, or 100 μg/kg, oral gavage) using rat models of cocaine fixed-ratio (FR) self-administration (SA), cocaine progressive-ratio (PR) SA, and sucrose pellet SA. In single-dosing treatment paradigm, cebranopadol significantly and dose-dependently reduced cocaine SA under FR and PR schedules and suppressed food intake under FR schedule without causing apparent side effects. In repeated-dosing treatment scheme, i.e. daily administration of 25, 50, 75, or 100 μg/kg cebranopadol for a week, the similar reduction in cocaine intake was detected, while non-negligible complications/side effects were observed at repeated high doses (75 and 100 μg/kg). The observed side effects were similar to the common toxic signs elicited by heroin at high doses, although cebranopadol did not fully substitute heroin's discriminative stimulant effects in our drug discriminative tests. These results demonstrated that the most appropriate oral dose of cebranopadol to balance the efficacy and safety is 50 μg/kg. Collectively, although cebranopadol may serve as a new treatment for cocaine dependence, more consideration, cautiousness, and a clear optimal dose window to dissociate its therapeutic effects from opioid side effects/complications in male and female subjects will be necessary to increase its practical clinical utility.

The role of 6-acetylmorphine in heroin-induced reward and locomotor sensitization in mice

We have previously demonstrated that heroin's first metabolite, 6-acetylmorphine (6-AM), is an important mediator of heroin's acute effects. However, the significance of 6-AM to the rewarding properties of heroin still remains unknown. The present study therefore aimed to examine the contribution of 6-AM to heroin-induced reward and locomotor sensitization. Mice were tested for conditioned place preference (CPP) induced by equimolar doses of heroin or 6-AM (1.25-5 μmol/kg). Psychomotor activity was recorded during the CPP conditioning sessions for assessment of drug-induced locomotor sensitization. The contribution of 6-AM to heroin reward and locomotor sensitization was further examined by pretreating mice with a 6-AM specific antibody (anti-6-AM mAb) 24 hours prior to the CPP procedure. Both heroin and 6-AM induced CPP in mice, but heroin generated twice as high CPP scores compared with 6-AM. Locomotor sensitization was expressed after repeated exposure to 2.5 and 5 μmol/kg heroin or 6-AM, but not after 1.25 μmol/kg, and we found no correlation between the expression of CPP and the magnitude of locomotor sensitization for either opioid. Pretreatment with anti-6-AM mAb suppressed both heroin-induced and 6-AM-induced CPP and locomotor sensitization. These findings provide evidence that 6-AM is essential for the rewarding and sensitizing properties of heroin; however, heroin caused stronger reward compared with 6-AM. This may be explained by the higher lipophilicity of heroin, providing more efficient drug transfer to the brain, ensuring rapid increase in the brain 6-AM concentration.

The influence of carboxylesterase 1 polymorphism and cannabidiol on the hepatic metabolism of heroin

Heroin (diamorphine) is a highly addictive opioid drug synthesized from morphine. The use of heroin and incidence of heroin associated overdose death has increased sharply in the US. Heroin is primarily metabolized via deacetylation (hydrolysis) forming the active metabolites 6-monoacetylmorphine (6-MAM) and morphine. A diminution in heroin hydrolysis is likely to cause higher drug effects and toxicities. In this study, we sought to determine the contribution of the major hepatic hydrolase carboxylesterase 1 (CES1) to heroin metabolism in the liver as well as the potential influence of one of its known genetic variants, G143E (rs71647871). Furthermore, given the potential therapeutic application of cannabidiol (CBD) for heroin addiction and the frequent co-abuse of cannabis and heroin, we also assessed the effects of CBD on heroin metabolism. In vitro systems containing human liver, wild-type CES1, and G143E CES1 S9 fractions were utilized in the assessment. The contribution of CES1 to the hydrolysis of heroin to 6-MAM was determined as 3.66%, and CES1 was unable to further catalyze 6-MAM under our assay conditions. The G143E variant showed a 3.2-fold lower intrinsic clearance of heroin as compared to the WT. CBD inhibited heroin and 6-MAM hydrolysis in a reversible manner, with IC₅₀s of 14.7 and 12.1 μM, respectively. Our study results suggested only minor involvement of CES1 in heroin hydrolysis in the liver. Therefore, the G143E variant is unlikely to cause significant impact despite a much lower hydrolytic activity. CBD exhibited potent in vitro inhibition toward both heroin and 6-MAM hydrolysis, which may be of potential clinical relevance.

Effectiveness and selectivity of a heroin conjugate vaccine to attenuate heroin, 6-acetylmorphine, and morphine antinociception in rats: Comparison with naltrexone

BACKGROUND

One emerging strategy to address the opioid crisis includes opioid-targeted immunopharmacotherapies. This study compared effectiveness of a heroin-tetanus toxoid (TT) conjugate vaccine to antagonize heroin, 6-acetylmorphine (6-AM), morphine, and fentanyl antinociception in rats.

METHODS

Adult male and female Sprague Dawley rats received three doses of active or control vaccine at weeks 0, 2, and 4. Vaccine pharmacological selectivity was assessed by comparing opioid dose-effect curves in 50 °C  warm-water tail-withdrawal procedure before and after active or control heroin-TT vaccine. Route of heroin administration [subcutaneous (SC) vs. intravenous [IV)] was also examined as a determinant of vaccine effectiveness. Continuous naltrexone treatment (0.0032-0.032 mg/kg/h) effects on heroin, 6-AM, and morphine antinociceptive potency were also determined as a benchmark for minimal vaccine effectiveness.

RESULTS

The heroin-TT vaccine decreased potency of SC heroin (5-fold), IV heroin (3-fold), and IV 6-AM (3-fold) for several weeks without affecting IV morphine or SC and IV fentanyl potency. The control vaccine did not alter potency of any opioid. Naltrexone dose-dependently decreased antinociceptive potency of SC heroin, and treatment with 0.01 mg/kg/h naltrexone produced similar, approximate 8-fold decreases in potencies of SC and IV heroin, IV 6-AM, and IV morphine. The combination of naltrexone and active vaccine was more effective than naltrexone alone to antagonize SC heroin but not IV heroin.

CONCLUSIONS

The heroin-TT vaccine formulation examined is less effective, but more selective, than chronic naltrexone to attenuate heroin antinociception in rats. Furthermore, these results provide an empirical framework for future preclinical opioid vaccine research to benchmark effectiveness against naltrexone.

6-Monoacetylmorphine (6-MAM), Not Morphine, Is Responsible for the Rapid Neural Effects Induced by Intravenous Heroin

Heroin rapidly enters the CNS but is quickly metabolized into 6-monoacetylmorphine (6-MAM) and then morphine. Although morphine is often thought to mediate heroin's neural effects, pharmacokinetic data question this view. To further understand the effects of heroin and its metabolites, oxygen sensors were used to examine changes in nucleus accumbens (NAc) oxygen levels. Heroin, 6-MAM, and morphine were all administered intravenously at two human-relevant doses (0.25 μmol/kg and 0.98 μmol/kg) in freely moving rats. Intravenous heroin induced a biphasic change in NAc oxygen, with a decrease resulting from respiratory depression and an increase resulting from cerebral vasodilation. 6-MAM caused similar but more rapid and slightly weaker effects  than heroin. The stronger response to heroin can be primarily attributed to heroin's permeability and metabolism resulting in more 6-MAM in the brain. Morphine only induced weak increases in NAc oxygen. Therefore, it appears that 6-MAM is the major contributor to acute neural effects induced by iv heroin.

Opioid Neurobiology, Neurogenetics and Neuropharmacology in Zebrafish

Despite the high prevalence of medicinal use and abuse of opioids, their neurobiology and mechanisms of action are not fully understood. Experimental (animal) models are critical for improving our understanding of opioid effects in vivo. As zebrafish (Danio rerio) are increasingly utilized as a powerful model organism in neuroscience research, mounting evidence suggests these fish as a useful tool to study opioid neurobiology. Here, we discuss the zebrafish opioid system with specific focus on opioid gene expression, existing genetic models, as well as its pharmacological and developmental regulation. As many human brain diseases involve pain and aberrant reward, we also summarize zebrafish models relevant to opioid regulation of pain and addiction, including evidence of functional interplay between the opioid system and central dopaminergic and other neurotransmitter mechanisms. Additionally, we critically evaluate the limitations of zebrafish models for translational opioid research and emphasize their developing utility for improving our understanding of evolutionarily conserved mechanisms of pain-related, addictive, affective and other behaviors, as well as for fostering opioid-related drug discovery.

The active heroin metabolite 6-acetylmorphine has robust reinforcing effects as assessed by self-administration in the rat

Previous studies have suggested that at least some of the behavioral effects of heroin might be mediated by its active metabolite 6-acetylmorphine (6-AM). The aim of the present study was to investigate the reinforcing effects of 6-AM and its role in mediating those of heroin. We used an intravenous self-administration procedure in male Sprague-Dawley rats including four phases: acquisition, extinction, reinstatement of drug-seeking, and re-acquisition. Independent groups of rats readily learned to self-administer equimolar doses (0.135 μmol/kg) of either 6-AM (44.3 μg/kg) or heroin (50 μg/kg). Under a fixed ratio 1 (FR1) schedule of reinforcement, the rate of responding was the same for 6-AM and heroin, but it was significantly higher for 6-AM than for heroin under a FR2 schedule. A non-contingent infusion ('priming') of 0.068 μmol/kg of either 6-AM or heroin reinstated non-reinforced drug-seeking (relapse). The rats readily re-acquired self-administration behaviour when given access to one of two doses (0.068 and 0.135 μmol/kg) of 6-AM or heroin. Pretreatment with a specific monoclonal antibody (mAb) against 6-AM blocked the priming effect of 6-AM, and modified the rate of lever-pressing on re-acquisition of 6-AM self-administration in a manner compatible with a shift to the right of the dose-effect curve. The mAb did not affect heroin responding. The present results show that 6-AM possesses reinforcing effects similar to those of heroin. The lack of effect of 6-AM mAb on heroin priming and heroin self-administration calls for further studies to clarify the role of heroin and its metabolites in heroin reward. This article is part of the Special Issue entitled 'Opioid Neuropharmacology: Advances in treating pain and opioid addiction'.

Blocking drug activation as a therapeutic strategy to attenuate acute toxicity and physiological effects of heroin

Heroin is a growing national crisis in America. There is an increasing frequency of heroin overdoses. All of the currently used therapeutic approaches to treatment of heroin abuse and other opioid drugs of abuse focus on antagonizing a brain receptor (particularly µ-opiate receptors). However, it has been known that the therapeutic use of certain µ-opiate receptor antagonist may actually increase heroin overdose. Once overdosed, heroin addicts may continue to get overdosed again and again until fatal. Here we report our design and validation of a novel therapeutic strategy targeting heroin activation based on our analysis of the chemical transformation and functional change of heroin in the body. An effective blocker of heroin activation, such as ethopropazine tested in this study, may be used as a standalone therapy or in combination with a currently available, traditional medications targeting µ-opiate receptors (e.g. naltrexone or its extended-release formulation Vivitrol). The combination therapy would be ideal for heroin abuse treatment as the effects of two therapeutic agents targeting two independent mechanisms are cooperative.

A computational strategy for finding novel targets and therapeutic compounds for opioid dependence

Opioids are widely used for treating different types of pains, but overuse and abuse of prescription opioids have led to opioid epidemic in the United States. Besides analgesic effects, chronic use of opioid can also cause tolerance, dependence, and even addiction. Effective treatment of opioid addiction remains a big challenge today. Studies on addictive effects of opioids focus on striatum, a main component in the brain responsible for drug dependence and addiction. Some transcription regulators have been associated with opioid addiction, but relationship between analgesic effects of opioids and dependence behaviors mediated by them at the molecular level has not been thoroughly investigated. In this paper, we developed a new computational strategy that identifies novel targets and potential therapeutic molecular compounds for opioid dependence and addiction. We employed several statistical and machine learning techniques and identified differentially expressed genes over time which were associated with dependence-related behaviors after exposure to either morphine or heroin, as well as potential transcription regulators that regulate these genes, using time course gene expression data from mouse striatum. Moreover, our findings revealed that some of these dependence-associated genes and transcription regulators are known to play key roles in opioid-mediated analgesia and tolerance, suggesting that an intricate relationship between opioid-induce pain-related pathways and dependence may develop at an early stage during opioid exposure. Finally, we determined small compounds that can potentially target the dependence-associated genes and transcription regulators. These compounds may facilitate development of effective therapy for opioid dependence and addiction. We also built a database (http://daportals.org) for all opioid-induced dependence-associated genes and transcription regulators that we discovered, as well as the small compounds that target those genes and transcription regulators.

A Monoclonal Antibody against 6-Acetylmorphine Protects Female Mice Offspring from Adverse Behavioral Effects Induced by Prenatal Heroin Exposure

Escalating opioid use among fertile women has increased the number of children being exposed to opioids during fetal life. Furthermore, accumulating evidence links prenatal opioid exposure, including opioid maintenance treatment, to long-term negative effects on cognition and behavior, and presses the need to explore novel treatment strategies for pregnant opioid users. The present study examined the potential of a monoclonal antibody (mAb) targeting heroin's first metabolite, 6-acetylmorphine (6-AM), in providing fetal protection against harmful effects of prenatal heroin exposure in mice. First, we examined anti-6-AM mAb's ability to block materno-fetal transfer of active metabolites after maternal heroin administration. Next, we studied whether maternal mAb pretreatment could prevent adverse effects in neonatal and adolescent offspring exposed to intrauterine heroin (3 × 1.05 mg/kg). Anti-6-AM mAb pretreatment of pregnant dams profoundly reduced the distribution of active heroin metabolites to the fetal brain. Furthermore, maternal mAb administration prevented hyperactivity and drug sensitization in adolescent female offspring prenatally exposed to heroin. Our findings demonstrate that passive immunization with a 6-AM-specific antibody during pregnancy provides fetal neuroprotection against heroin metabolites, and thereby prevents persistent adverse behavioral effects in the offspring. An immunotherapeutic approach to protect the fetus against long-term effects of prenatal drug exposure has not been reported previously, and should be further explored as prophylactic treatment of pregnant heroin users susceptible to relapse.

Stable isotope-labelled morphine to study in vivo central and peripheral morphine glucuronidation and brain transport in tolerant mice

BACKGROUND AND PURPOSE

Chronic administration of medication can significantly affect metabolic enzymes leading to physiological adaptations. Morphine metabolism in the liver has been extensively studied following acute morphine treatment, but such metabolic processes in the CNS are poorly characterized. Long-term morphine treatment is limited by the development of tolerance, resulting in a decrease of its analgesic effect. Whether or not morphine analgesic tolerance affects in vivo brain morphine metabolism and blood-brain barrier (BBB) permeability remains a major question. Here, we have attempted to characterize the in vivo metabolism and BBB permeability of morphine after long-term treatment, at both central and peripheral levels.

EXPERIMENTAL APPROACH

Male C57BL/6 mice were injected with morphine or saline solution for eight consecutive days in order to induce morphine analgesic tolerance. On the ninth day, both groups received a final injection of morphine (85%) and d3-morphine (morphine bearing three ² H; 15%, w/w). Mice were then killed and blood, urine, brain and liver samples were collected. LC-MS/MS was used to quantify morphine, its metabolite morphine-3-glucuronide (M3G) and their respective d3-labelled forms.

KEY RESULTS

We found no significant differences in morphine CNS uptake and metabolism between control and tolerant mice. Interestingly, d3-morphine metabolism was decreased compared to morphine without any interference with our study.

CONCLUSIONS AND IMPLICATIONS

Our data suggests that tolerance to the analgesic effects of morphine is not linked to increased glucuronidation to M3G or to altered global BBB permeability of morphine.

Kinetic characterization of cholinesterases and a therapeutically valuable cocaine hydrolase for their catalytic activities against heroin and its metabolite 6-monoacetylmorphine

As the most popularly abused one of opioids, heroin is actually a prodrug. In the body, heroin is hydrolyzed/activated to 6-monoacetylmorphine (6-MAM) first and then to morphine to produce its toxic and physiological effects. It has been known that heroin hydrolysis to 6-MAM and morphine is accelerated by cholinesterases, including acetylcholinesterase (AChE) and/or butyrylcholinesterase (BChE). However, there has been controversy over the specific catalytic activities and functional significance of the cholinesterases, which requires for the more careful kinetic characterization under the same experimental conditions. Here we report the kinetic characterization of AChE, BChE, and a therapeutically promising cocaine hydrolase (CocH1) for heroin and 6-MAM hydrolyses under the same experimental conditions. It has been demonstrated that AChE and BChE have similar k_cat values (2100 and 1840 min^-1, respectively) against heroin, but with a large difference in K_M (2170 and 120 μM, respectively). Both AChE and BChE can catalyze 6-MAM hydrolysis to morphine, with relatively lower catalytic efficiency compared to the heroin hydrolysis. CocH1 can also catalyze hydrolysis of heroin (k_cat = 2150 min^-1 and K_M = 245 μM) and 6-MAM (k_cat = 0.223 min^-1 and K_M = 292 μM), with relatively larger K_M values and lower catalytic efficiency compared to BChE. Notably, the K_M values of CocH1 against both heroin and 6-MAM are all much larger than previously reported maximum serum heroin and 6-MAM concentrations observed in heroin users, implying that the heroin use along with cocaine will not drastically affect the catalytic activity of CocH1 against cocaine in the CocH1-based enzyme therapy for cocaine abuse.

A Stable Heroin Analogue That Can Serve as a Vaccine Hapten to Induce Antibodies That Block the Effects of Heroin and Its Metabolites in Rodents and That Cross-React Immunologically with Related Drugs of Abuse

An improved synthesis of a haptenic heroin surrogate 1 (6-AmHap) is reported. The intermediate needed for the preparation of 1 was described in the route in the synthesis of 2 (DiAmHap). A scalable procedure was developed to install the C-3 amido group. Using the Boc protectng group in 18 allowed preparation of 1 in an overall yield of 53% from 4 and eliminated the necessity of preparing the diamide 13. Hapten 1 was conjugated to tetanus toxoid and mixed with liposomes containing monophosphoryl lipid A as an adjuvant. The 1 vaccine induced high anti-1 IgG levels that reduced heroin-induced antinociception and locomotive behavioral changes following repeated subcutaneous and intravenous heroin challenges in mice and rats. Vaccinated mice had reduced heroin-induced hyperlocomotion following a 50 mg/kg heroin challenge. The 1 vaccine-induced antibodies bound to heroin and other abused opioids, including hydrocodone, oxycodone, hydromorphone, oxymorphone, and codeine.

Conjugate Vaccine Immunotherapy for Substance Use Disorder

Substance use disorder, especially in relation to opioids such as heroin and fentanyl, is a significant public health issue and has intensified in recent years. As a result, substantial interest exists in developing therapeutics to counteract the effects of abused drugs. A promising universal strategy for antagonizing the pharmacology of virtually any drug involves the development of a conjugate vaccine, wherein a hapten structurally similar to the target drug is conjugated to an immunogenic carrier protein. When formulated with adjuvants and immunized, the immunoconjugate should elicit serum IgG antibodies with the ability to sequester the target drug to prevent its entry to the brain, thereby acting as an immunoantagonist. Despite the failures of first-generation conjugate vaccines against cocaine and nicotine in clinical trials, second-generation vaccines have shown dramatically improved performance in preclinical models, thus renewing the potential clinical utility of conjugate vaccines in curbing substance use disorder. This review explores the critical design elements of drug conjugate vaccines such as hapten structure, adjuvant formulation, bioconjugate chemistry, and carrier protein selection. Methods for evaluating these vaccines are discussed, and recent progress in vaccine development for each drug is summarized.

Pharmacoepigenomics of opiates and methadone maintenance treatment: current data and perspectives

Current treatments of opioid addiction include primarily maintenance medications such as methadone. Chronic exposure to opiate and/or long-lasting maintenance treatment induce modulations of gene expression in brain and peripheral tissues. There is increasing evidence that epigenetic modifications underlie these modulations. This review summarizes published results on opioid-induced epigenetic changes in animal models and in patients. The epigenetic modifications observed with other drugs of abuse often used by opiate abusers are also outlined. Specific methadone maintenance treatment induced epigenetic modifications at different treatment stages may be combined with the ones resulting from patients’ substance use history. Therefore, research comparing groups of addicts with similar history and substances use disorders but contrasting for well-characterized treatment phenotypes should be encouraged.

Development of a Clinically Viable Heroin Vaccine

Heroin is a highly abused opioid and incurs a significant detriment to society worldwide. In an effort to expand the limited pharmacotherapy options for opioid use disorders, a heroin conjugate vaccine was developed through comprehensive evaluation of hapten structure, carrier protein, adjuvant and dosing. Immunization of mice with an optimized heroin-tetanus toxoid (TT) conjugate formulated with adjuvants alum and CpG oligodeoxynucleotide (ODN) generated heroin "immunoantagonism", reducing heroin potency by >15-fold. Moreover, the vaccine effects proved to be durable, persisting for over eight months. The lead vaccine was effective in rhesus monkeys, generating significant and sustained antidrug IgG titers in each subject. Characterization of both mouse and monkey antiheroin antibodies by surface plasmon resonance (SPR) revealed low nanomolar antiserum affinity for the key heroin metabolite, 6-acetylmorphine (6AM), with minimal cross reactivity to clinically used opioids. Following a series of heroin challenges over six months in vaccinated monkeys, drug-sequestering antibodies caused marked attenuation of heroin potency (>4-fold) in a schedule-controlled responding (SCR) behavioral assay. Overall, these preclinical results provide an empirical foundation supporting the further evaluation and potential clinical utility of an effective heroin vaccine in treating opioid use disorders.

Heroin-HIV-1 (H2) vaccine: induction of dual immunologic effects with a heroin hapten-conjugate and an HIV-1 envelope V2 peptide with liposomal lipid A as an adjuvant

A synthetic heroin analog (MorHap) and a synthetic 42 amino acid V2 loop peptide from A/E strain of HIV-1 gp120 envelope protein that was previously used in a successful phase III vaccine trial were constructed as antigens together with liposomes containing monophosphoryl lipid A as an adjuvant, to explore the feasibility of producing a dual use vaccine both for treatment of heroin addiction and prevention of HIV-1 infection among injection drug users. The V2 peptide was tethered by a palmitoyl fatty acyl tail embedded in the liposomal lipid bilayer, and the heroin analog was conjugated to tetanus toxoid as a carrier protein that was mixed with the adjuvant. Upon comparison of a linear V2 peptide with a cyclic peptide, differences were found in the secondary configurations by circular dichroism, with the tethered cyclic peptide (palm-cyclic peptide) entirely in a random coil, and the tethered linear V2 peptide (palm-linear V2 peptide) entirely in a beta-sheet. Upon immunization of mice, palm-cyclic peptide induced anti-cyclic peptide endpoint titers >10⁶ and was considered to be a better immunogen overall than palm-linear V2 peptide for inducing antibodies to gp120 and gp70-V1V2. The antibodies also inhibited the binding of V2 peptide to the HIV-1 α₄β₇ integrin receptor. Antibody titers to MorHap, even with the presence of injected cyclic peptide, were very high, and resulted in inhibition of the hyper-locomotion and antinociception effects of injected heroin. From these initial experiments, we conclude that with a potent adjuvant and mostly synthetic constituents, a vaccine directed to heroin and HIV-1 (H2 vaccine) could be a feasible objective.

A vaccine designed to treat heroin addiction while at the same time preventing HIV infection elicited strong immune responses in mice. Scientists from the US government led by Carl Alving from the Walter Reed Army Institute of Research in Bethesda, Maryland, created a dual vaccine formulated with three main components: a segment of a protein expressed on the surface of HIV; synthetic molecules that resemble heroin and its degradation products; and a potent adjuvant to stimulate the immune system. Mice immunized with this vaccine had high antibody titers against the HIV surface protein as well as heroin and its derivatives. These mice also showed dulled responses to injected heroin. The findings suggest this vaccine strategy could help fight heroin abuse and the high risk of HIV infection among intravenous drug users.

Metabolomic profiling of brain tissues of mice chronically exposed to heroin

The chronic neurotoxicity of heroin on the nervous system is poorly understood. To address this issue, we comprehensively assessed the alteration of brain metabolomics caused by chronic heroin exposure and the withdrawal of heroin. Male C57BL/6J mice (n = 10) were given heroin (15 μmol/kg, i.p., twice a day) for 12 days while the withdrawal group received saline-treatment instead of heroin for the last two days. The control group received saline. We developed an UPLC-TOF/MS-based metabolomic approach to analyze the metabolites and carry out a metabolic pathway analysis in the brain. The major metabolites contributing to the discrimination were identified as amino acids, tricarboxylic-acid cycle intermediates, neurotransmitters, nucleotides and other compounds. A marked reduction in histidine and a slight but significant increase in phenylalanine and tryptophan were observed after heroin was withdrawn while the increased level of catecholamines was restored to baseline. Interestingly, N-acetylserotonin - a precursor of melatonin - was increased with the withdrawal of heroin while melatonin was markedly reduced along with the sub-chronic exposure to heroin. This shows that heroin disrupts not only the energy metabolism but also the biosynthesis of both catecholamines and melatonin in the mouse brain. Therefore, these substances are candidate biomarkers for chronic heroin-abuse.

Comparison of (+)- and (-)-Naloxone on the Acute Psychomotor-Stimulating Effects of Heroin, 6-Acetylmorphine, and Morphine in Mice

Toll-like receptor 4 (TLR4) signaling is implied in opioid reinforcement, reward, and withdrawal. Here, we explored whether TLR4 signaling is involved in the acute psychomotor-stimulating effects of heroin, 6-acetylmorphine (6-AM), and morphine as well as whether there are differences between the three opioids regarding TLR4 signaling. To address this, we examined how pretreatment with (+)-naloxone, a TLR4 active but opioid receptor (OR) inactive antagonist, affected the acute increase in locomotor activity induced by heroin, 6-AM, or morphine in mice. We also assessed the effect of pretreatment with (-)-naloxone, a TLR4 and OR active antagonist, as well as the pharmacokinetic profiles of (+) and (-)-naloxone in the blood and brain. We found that (-)-naloxone reduced acute opioid-induced locomotor activity in a dose-dependent manner. By contrast, (+)-naloxone, administered in doses assumed to antagonize TLR4 but not ORs, did not affect acute locomotor activity induced by heroin, 6-AM, or morphine. Both naloxone isomers exhibited similar concentration versus time profiles in the blood and brain, but the brain concentrations of (-)-naloxone reached higher levels than those of (+)-naloxone. However, the discrepancies in their pharmacokinetic properties did not explain the marked difference between the two isomers' ability to affect opioid-induced locomotor activity. Our results underpin the importance of OR activation and do not indicate an apparent role of TLR4 signaling in acute opioid-induced psychomotor stimulation in mice. Furthermore, there were no marked differences between heroin, 6-AM, and morphine regarding involvement of OR or TLR4 signaling.

Pharmacological Effects of a Monoclonal Antibody against 6-Monoacetylmorphine upon Heroin-Induced Locomotor Activity and Pharmacokinetics in Mice

Immunotherapy can provide a supplemental treatment strategy against heroin use on the principle of sequestering the active drug in the bloodstream, thereby reducing its distribution to the brain. Previous studies have shown that heroin's first metabolite, 6-monoacetylmorphine (6-MAM), is the main mediator of acute heroin effects. The objective of the present study was to characterize the pharmacological potential of a monoclonal antibody against 6-MAM (anti-6-MAM mAb) to counteract the heroin response. The individual contributions from heroin and 6-MAM to heroin effects were also examined by pretreating mice with anti-6-MAM mAb (10-100 mg/kg) prior to either heroin or 6-MAM injection (1.25-2.5 μmol/kg). The opioid-induced behavioral response was assessed in a locomotor activity test, followed by opioid and antibody quantification in blood and brain tissue. Pretreatment with mAb caused a profound reduction of heroin- and 6-MAM-induced behavior, accompanied by correspondingly decreased levels of 6-MAM in brain tissue. mAb pretreatment was more efficient against 6-MAM injection than against heroin, leading to an almost complete blockade of 6-MAM-induced effects. mAb pretreatment was unable to block the immediate (5-minute) transport of active metabolites across the blood-brain barrier after heroin injection, indicating that heroin itself appears to enhance the immediate delivery of 6-MAM to the brain. The current study provides additional evidence that 6-MAM sequestration is crucial for counteracting the acute heroin response, and demonstrates the pharmacological potential of immunotherapy against heroin use.

Pharmacokinetics of heroin and its metabolites in vitreous humor and blood in a living pig model

Vitreous humor (VH) is an alternative matrix for drug analysis in forensic toxicology. However, little is known about the distribution of xenobiotics, such as opioids, into VH in living organisms. The aim of this study was to simultaneously measure heroin and metabolite concentrations in blood and VH after injection of heroin in a living pig model. Six pigs were under non-opioid anesthesia during the surgical operation and experiment. Ocular microdialysis was used to acquire dialysate from VH, and a venous catheter was used for blood sampling. Twenty milligrams of heroin was injected intravenously with subsequent sampling of blood and dialysate for 6 h. The samples were analyzed by ultra-performance liquid chromatography–tandem mass spectrometry. Heroin was not detected in VH; 6-monoacetylmorphine (6-MAM) and morphine were first detected in VH after 60 min. The morphine concentration in VH thereafter increased throughout the experimental period. For 6-MAM, C_max was reached after 230 min in VH. In blood, 6-MAM reached C_max after 0.5 min, with a subsequent biphasic elimination phase. The blood and VH 6-MAM concentrations reached equilibrium after 2 h. In blood, morphine reached C_max after 4.3 min, with a subsequent slower elimination than 6-MAM. The blood and VH morphine concentrations were in equilibrium about 6 h after injection of heroin. In conclusion, both 6-MAM and morphine showed slow transport into VH; detection of 6-MAM in VH did not necessarily reflect a recent intake of heroin. Because postmortem changes are expected to be small in VH, these experimental results could assist the interpretation of heroin deaths.

On the effects of the basis set superposition error on the change of QTAIM charges in adduct formation. Application to complexes between morphine and cocaine and their main metabolites

QTAIM atomic properties variation upon interaction is analyzed by: (i) deformation; (ii) BSSE estimated by counterpoise method; and (iii) binding.

Dissociation of heroin-induced emotional dysfunction from psychomotor activation and physical dependence among inbred mouse strains

RATIONALE

Opiate addiction is a brain disorder emerging through repeated intoxication and withdrawal episodes. Epidemiological studies also indicate that chronic exposure to opiates may lead in susceptible individuals to the emergence of depressive symptoms, strongly contributing to the severity and chronicity of addiction. We recently established a mouse model of heroin abstinence, characterized by the development of depressive-like behaviors following chronic heroin exposure.

OBJECTIVES

While genetic factors regulating immediate behavioral responses to opiates have been largely investigated, little is known about their contribution to long-term emotional regulation during abstinence. Here, we compared locomotor stimulation and physical dependence induced by heroin exposure, as well as emotional dysfunction following abstinence, across mice strains with distinct genetic backgrounds.

METHODS

Mice from three inbred strains (C57BL/6J, Balb/cByJ, and 129S2/SvPas) were exposed to an escalating chronic heroin regimen (10-50 mg/kg). Independent cohorts were used to assess drug-induced locomotor activity during chronic treatment, naloxone-precipitated withdrawal at the end of chronic treatment, and emotional-like responses after a 4-week abstinence period.

RESULTS

Distinct behavioral profiles were observed across strains during heroin treatment, with no physical dependence and low locomotor stimulation in 129S2/SvPas. In addition, different behavioral impairments developed during abstinence across the three strains, with increased despair-like behavior in 129S2/SvPas and Balb/cByJ, and low sociability in 129S2/SvPas and C57BL/6J.

CONCLUSIONS

Our results indicate that depressive-like behaviors emerge during heroin abstinence, whatever the severity of immediate behavioral responses to the drug. In addition, inbred mouse strains will allow studying several aspects of mood-related deficits associated with addiction.

Transporter-Mediated Disposition of Opioids: Implications for Clinical Drug Interactions

Opioid-related deaths, abuse, and drug interactions are growing epidemic problems that have medical, social, and economic implications. Drug transporters play a major role in the disposition of many drugs, including opioids; hence they can modulate their pharmacokinetics, pharmacodynamics and their associated drug-drug interactions (DDIs). Our understanding of the interaction of transporters with many therapeutic agents is improving; however, investigating such interactions with opioids is progressing relatively slowly despite the alarming number of opioids-mediated DDIs that may be related to transporters. This review presents a comprehensive report of the current literature relating to opioids and their drug transporter interactions. Additionally, it highlights the emergence of transporters that are yet to be fully identified but may play prominent roles in the disposition of opioids, the growing interest in transporter genomics for opioids, and the potential implications of opioid-drug transporter interactions for cancer treatments. A better understanding of drug transporters interactions with opioids will provide greater insight into potential clinical DDIs and could help improve opioids safety and efficacy.

Diffusivity of the uncinate fasciculus in heroin users relates to their levels of anxiety

Heroin use is closely associated with emotional dysregulation, which may explain its high comorbidity with disorders such as anxiety and depression. However, the understanding of the neurobiological etiology of the association between heroin use and emotional dysregulation is limited. Previous studies have suggested an impact of heroin on diffusivity in white matter involving the emotional regulatory system, but the specificity of this finding remains to be determined. Therefore, this study investigated the association between heroin use and diffusivity of white matter tracts in heroin users and examined whether the tracts were associated with their elevated anxiety and depression levels. A sample of 26 right-handed male abstinent heroin users (25 to 42 years of age) and 32 matched healthy controls (19 to 55 years of age) was recruited for this study. Diffusion tensor imaging data were collected, and their levels of anxiety and depression were assessed using the Hospital Anxiety and Depression Scale. Our findings indicated that heroin users exhibited higher levels of anxiety and depression, but the heroin use-associated left uncinate fasciculus was only related to their anxiety level, suggesting that association between heroin and anxiety has an incremental organic basis but that for depression could be a threshold issue. This finding improves our understanding of heroin addiction and its comorbid affective disorder and facilitates future therapeutic development.

Pharmacokinetic correlates of the effects of a heroin vaccine on heroin self-administration in rats

The purpose of this study was to evaluate the effects of a morphine-conjugate vaccine (M-KLH) on the acquisition, maintenance, and reinstatement of heroin self-administration (HSA) in rats, and on heroin and metabolite distribution during heroin administration that approximated the self-administered dosing rate. Vaccination with M-KLH blocked heroin-primed reinstatement of heroin responding. Vaccination also decreased HSA at low heroin unit doses but produced a compensatory increase in heroin self-administration at high unit doses. Vaccination shifted the heroin dose-response curve to the right, indicating reduced heroin potency, and behavioral economic demand curve analysis further confirmed this effect. In a separate experiment heroin was administered at rates simulating heroin exposure during HSA. Heroin and its active metabolites, 6-acetylmorphine (6-AM) and morphine, were retained in plasma and metabolite concentrations were reduced in brain in vaccinated rats compared to controls. Reductions in 6-AM concentrations in brain after vaccination were consistent with the changes in HSA rates accompanying vaccination. These data provide evidence that 6-AM is the principal mediator of heroin reinforcement, and the principal target of the M-KLH vaccine, in this model. While heroin vaccines may have potential as therapies for heroin addiction, high antibody to drug ratios appear to be important for obtaining maximal efficacy.

Reaction pathways and free energy profiles for cholinesterase-catalyzed hydrolysis of 6-monoacetylmorphine

As the most active metabolite of heroin, 6-monoacetylmorphine (6-MAM) can penetrate into the brain for the rapid onset of heroin effects. The primary enzymes responsible for the metabolism of 6-MAM to the less potent morphine in humans are acetylcholinesterase (AChE) and butyrylcholinesterase (BChE). The detailed reaction pathways for AChE- and BChE-catalyzed hydrolysis of 6-MAM to morphine have been explored, for the first time, in the present study by performing first-principles quantum mechanical/molecular mechanical free energy calculations. It has been demonstrated that the two enzymatic reaction processes follow similar catalytic reaction mechanisms, and the whole catalytic reaction pathway for each enzyme consists of four reaction steps. According to the calculated results, the second reaction step associated with the transition state TS2(a)/TS2(b) should be rate-determining for the AChE/BChE-catalyzed hydrolysis, and the free energy barrier calculated for the AChE-catalyzed hydrolysis (18.3 kcal mol(-1)) is 2.5 kcal mol(-1) lower than that for the BChE-catalyzed hydrolysis (20.8 kcal mol(-1)). The free energy barriers calculated for the AChE- and BChE-catalyzed reactions are in good agreement with the experimentally derived activation free energies (17.5 and 20.7 kcal mol(-1) for the AChE- and BChE-catalyzed reactions, respectively). Further structural analysis reveals that the aromatic residues Phe295 and Phe297 in the acyl pocket of AChE (corresponding to Leu286 and Val288 in BChE) contribute to the lower energy of TS2(a) relative to TS2(b). The obtained structural and mechanistic insights could be valuable for use in future rational design of a novel therapeutic treatment of heroin abuse.