Influence of agonist induced internalization on [3H]Ro15-4513 binding-an application to imaging fluctuations in endogenous GABA with positron emission tomography.

Low affinity α1/α2 containing GABAA receptors are significantly less able to bind [(11) C]/[(3) H]Ro15-4513 following translocation to the endosomal environment. The alterations in [(11) C]Ro15-4513 binding observed in vivo following perturbations in endogenous GABA are likely driven by both alterations in receptor binding parameters following agonist induced internalisation and the GABA Shift.

Oral ethanol prescribing for alcohol withdrawal syndrome: initial findings and future directions following implementation within a United Kingdom National Health Service setting.

INTRODUCTION: Prescribing of ethanol may be an alternative to benzodiazepines for managing alcohol withdrawal syndrome. We present our experience of oral ethanol prescribing within an acute United Kingdom National Health Service setting. METHODS: A retrospective review of patients presenting with alcohol withdrawal who were managed with oral ethanol or benzodiazepines was performed from data collected across two acute care settings. Ethanol prescribing inclusion: high risk of delirium tremens, or a history of harmful alcohol consumption (typically ≥30 units/day; in which 1 unit = 8 grams of alcohol; one standard United States drink = 14 grams of alcohol) or known to have a history of severe alcohol withdrawal, alcohol-related seizures or delirium tremens. Inverse propensity score weighting was used to partially account for variance between the two patient populations. RESULTS: Fifty (82 per cent male; average age 50.9 years) and 93 (84 per cent male; average age 46.5 years) patients in receipt of benzodiazepines or ethanol, respectively, were included. The likelihood of hospital admission was significantly reduced when individuals were managed with ethanol (odds ratio 0.206 (95 per cent confidence interval; 0.066-0.641), Wald chi-square P = 0.006). In those not admitted, the treatment type had no significant impact on length of stay or the number of occasions a pharmacological agent was required. In those admitted, treatment had no significant effect on length of stay. DISCUSSION: We offer preliminary evidence to support a role of oral ethanol in the management of patients with alcohol withdrawal. We have implemented a robust and translatable guideline. Despite limitations in the data set the impact of ethanol in reducing the likelihood of admission remained significant. CONCLUSIONS: In individuals at significant risk of severe alcohol withdrawal, prescribing ethanol as part of a comprehensive care plan, may reduce unplanned admissions. The preliminary findings presented here warrant further assessment through prospective studies.

Alcohol-related brain damage: an umbrella (term) for the approaching post-COVID monsoon.

Individuals with alcohol-related brain damage (ARBD) represent a population whose healthcare needs often go unmet. This is the result of a lack of not only an awareness surrounding the condition by healthcare professionals, but also healthcare service inclusion and delivery, more broadly. The Coronavirus 2019 (COVID-19) pandemic and the associated lockdowns dramatically affected the accessibility and availability of addiction services globally, while also driving changes in alcohol consumption among the most vulnerable. In the absence of change, this culmination of increased high-risk drinking behaviour, lack of awareness by healthcare professionals and severely limited service delivery for individuals living with ARBD post COVID-19, represents a perfect storm that is rapidly approaching our health and care services world-wide. Collectively, this will reduce positive health outcomes in an already at-risk group.

Elective alcohol detoxification - a resource and efficacy evaluation.

An evaluation was performed to assess efficacy and resource utilisation of an elective inpatient alcohol detoxification service at a large inner-city teaching hospital. Abstinence rates at 3, 6 and 12 months post-detoxification were 68.1, 44.7 and 36.2%, respectively. Relapse was associated with referrals from acute hospital services, previous detoxifications, longer time between referral and admission for detoxification, presence of alcohol in the blood on the day of admission and requirement for benzodiazepines during withdrawal. The service operates within the national 18-week referral target and runs at a cost substantially lower than that of residential alcohol detoxification facilities but with similar sobriety rates. We demonstrate that elective detoxification with specialist follow-up provides an effective service both in terms of patient outcomes and resource use. Further investment in these services at both local and national level should be considered.

Nalmefene Reduces Reward Anticipation in Alcohol Dependence: An Experimental Functional Magnetic Resonance Imaging Study.

BACKGROUND: Nalmefene is a µ and δ opioid receptor antagonist, κ opioid receptor partial agonist that has recently been approved in Europe for treating alcohol dependence. It offers a treatment approach for alcohol-dependent individuals with "high-risk drinking levels" to reduce their alcohol consumption. However, the neurobiological mechanism underpinning its effects on alcohol consumption remains to be determined. Using a randomized, double-blind, placebo-controlled, within-subject crossover design we aimed to determine the effect of a single dose of nalmefene on striatal blood oxygen level-dependent (BOLD) signal change during anticipation of monetary reward using the monetary incentive delay task following alcohol challenge. METHODS: Twenty-two currently heavy-drinking, non-treatment-seeking alcohol-dependent males were recruited. The effect of single dose nalmefene (18 mg) on changes in a priori defined striatal region of interest BOLD signal change during reward anticipation compared with placebo was investigated using functional magnetic resonance imaging. Both conditions were performed under intravenous alcohol administration (6% vol/vol infusion to achieve a target level of 80 mg/dL). RESULTS: Datasets from 18 participants were available and showed that in the presence of the alcohol infusion, nalmefene significantly reduced the BOLD response in the striatal region of interest compared with placebo. Nalmefene did not alter brain perfusion. CONCLUSIONS: Nalmefene blunts BOLD response in the mesolimbic system during anticipation of monetary reward and an alcohol infusion. This is consistent with nalmefene's actions on opioid receptors, which modulate the mesolimbic dopaminergic system, and provides a neurobiological basis for its efficacy.

Imaging endogenous opioid peptide release with [11C]carfentanil and [3H]diprenorphine: influence of agonist-induced internalization.

Understanding the cellular processes underpinning the changes in binding observed during positron emission tomography neurotransmitter release studies may aid translation of these methodologies to other neurotransmitter systems. We compared the sensitivities of opioid receptor radioligands, carfentanil, and diprenorphine, to amphetamine-induced endogenous opioid peptide (EOP) release and methadone administration in the rat. We also investigated whether agonist-induced internalization was involved in reductions in observed binding using subcellular fractionation and confocal microscopy. After radioligand administration, significant reductions in [(11)C]carfentanil, but not [(3)H]diprenorphine, uptake were observed after methadone and amphetamine pretreatment. Subcellular fractionation and in vitro radioligand binding studies showed that amphetamine pretreatment only decreased total [(11)C]carfentanil binding. In vitro saturation binding studies conducted in buffers representative of the internalization pathway suggested that µ-receptors are significantly less able to bind the radioligands in endosomal compared with extracellular compartments. Finally, a significant increase in µ-receptor-early endosome co-localization in the hypothalamus was observed after amphetamine and methadone treatment using double-labeling confocal microscopy, with no changes in δ- or κ-receptor co-localization. These data indicate carfentanil may be superior to diprenorphine when imaging EOP release in vivo, and that alterations in the ability to bind internalized receptors may be a predictor of ligand sensitivity to endogenous neurotransmitter release.

The influence of different cellular environments on PET radioligand binding: an application to D2/3-dopamine receptor imaging.

Various D2/3 receptor PET radioligands are sensitive to endogenous dopamine release in vivo. The Occupancy Model is generally used to interpret changes in binding observed in in vivo competition binding studies; an Internalisation Hypothesis may also contribute to these changes in signal. Extension of in vivo competition imaging to other receptor systems has been relatively unsuccessful. A greater understanding of the cellular processes underlying signal changes following endogenous neurotransmitter release may help translate this imaging paradigm to other receptor systems. To investigate the Internalisation Hypothesis we assessed the effects of different cellular environments, representative of those experienced by a receptor following agonist-induced internalisation, on the binding of three D2/3 PET ligands with previously reported sensitivities to endogenous dopamine in vivo, namely [3H]spiperone, [3H]raclopride and [3H]PhNO. Furthermore, we determined the contribution of each cellular compartment to total striatal binding for these D2/3 ligands. These studies suggest that sensitivity to endogenous dopamine release in vivo is related to a decrease in affinity in the endosomal environment compared with those found at the cell surface. In agreement with these findings we also demonstrate that ∼25% of total striatal binding for [3H]spiperone originates from sub-cellular, microsomal receptors, whereas for [3H]raclopride and [3H]PhNO, this fraction is lower, representing ∼14% and 17%, respectively. This pharmacological approach is fully translatable to other receptor systems. Assessment of affinity shifts in different cellular compartments may play a crucial role for understanding if a radioligand is sensitive to endogenous release in vivo, for not just the D2/3, but other receptor systems.

Evaluation of 11C-BU99008, a PET ligand for the imidazoline2 binding sites in rhesus brain.

UNLABELLED: The development of a PET radioligand selective for I2-imidazoline binding sites (I2BS) would enable, for the first time, specific, measurable in vivo imaging of this target protein, along with assessment of alterations in expression patterns of this protein in disease pathophysiology. METHODS: BU99008 was identified as the most promising I2BS radioligand candidate and radiolabeled with (11)C via methylation. The in vivo binding properties of (11)C-BU99008 were assessed in rhesus monkeys to determine brain penetration, brain distribution, binding specificity and selectivity (via the use of the unlabeled blockers), and the most appropriate kinetic model for analyzing data generated with this PET radioligand. RESULTS: (11)C-BU99008 was demonstrated to readily enter the brain, resulting in a heterogeneous distribution (globus pallidus > cortical regions > cerebellum) consistent with the reported regional I2BS densities as determined by human tissue section autoradiography and preclinical in vivo PET studies in the pig. In vivo competition studies revealed that (11)C-BU99008 displayed reversible kinetics specific for the I2BS. The multilinear analysis (MA1) model was the most appropriate analysis method for this PET radioligand in this species. The selective I2BS blocker BU224 was shown to cause a saturable, dose-dependent decrease in (11)C-BU99008 binding in all regions of the brain assessed, further demonstrating the heterogeneous distribution of I2BS protein in the rhesus brain and binding specificity for this radioligand. CONCLUSION: These data demonstrate that (11)C-BU99008 represents a specific and selective PET radioligand for imaging and quantifying the I2BS, in vivo, in the rhesus monkey. Further work is under way to translate the use of (11)C-BU99008 to the clinic.

Endogenous opioid release in the human brain reward system induced by acute amphetamine administration.

BACKGROUND: We aimed to demonstrate a pharmacologically stimulated endogenous opioid release in the living human brain by evaluating the effects of amphetamine administration on [(11)C]carfentanil binding with positron emission tomography (PET). METHODS: Twelve healthy male volunteers underwent [(11)C]carfentanil PET before and 3 hours after a single oral dose of d-amphetamine (either a "high" dose, .5 mg/kg, or a sub-pharmacological "ultra-low" dose, 1.25 mg total dose or approximately .017 mg/kg). Reductions in [(11)C]carfentanil binding from baseline to post-amphetamine scans (ΔBP(ND)) after the "high" and "ultra-low" amphetamine doses were assessed in 10 regions of interest. RESULTS: [(11)C]carfentanil binding was reduced after the "high" but not the "ultra-low" amphetamine dose in the frontal cortex, putamen, caudate, thalamus, anterior cingulate, and insula. CONCLUSIONS: Our findings indicate that oral amphetamine administration induces endogenous opioid release in different areas of human brain, including basal ganglia, frontal cortex areas, and thalamus. The combination of an amphetamine challenge and [(11)C]carfentanil PET is a practical and robust method to probe the opioid system in the living human brain.