Daily THC and withdrawal increase dopamine D1-D2 receptor heteromer to mediate anhedonia and anxiogenic-like behavior through a dynorphin and kappa opioid receptor mechanism

Receptor dimers and biased ligands: Novel strategies for targeting G protein-coupled receptors

G protein-coupled receptors (GPCRs) are the largest superfamily of membrane receptors. They regulate physiological and pathological processes such as metabolic homeostasis, cell proliferation and differentiation, and the immune response, and are one of the most important classes of drug targets, being targeted by 30-40 % of marketed drugs. A growing number of studies continue to reveal the complexity of GPCRs, especially their ability to interact with each other to form higher-order structures such as homodimers and heterodimers, which have different functions than monomers, and are involved in disease development and progression. The existence of GPCR homodimers and heterodimers is opening up new directions in drug discovery and development to harness their therapeutic potential. Particularly striking is the ability of GPCR dimers to trigger unique biased signalling pathways, which exquisitely balance the relationship between therapeutic effects and side effects. By suppressing adverse reactions and enhancing beneficial drug effects, GPCR dimers provide an unprecedented opportunity to minimise side effects, maximise therapeutic efficacy and enhance safety. This review aims to highlight the latest research advances in GPCR dimerization and GPCR-biased signalling, focusing on the development of dimer-targeting and biased ligands as innovative drugs that will likely provide new strategies for treating GPCR-related diseases as well as a better understanding of drug design for compounds that target GPCRs. GPCRs will play an increasingly important role in precision medicine and personalised therapy, leading us towards a safer, more efficient and smarter pharmaceutical future.

The Dynorphin/-Opioid Receptor System at the Interface of Hyperalgesia/Hyperkatifeia and Addiction

Purpose of Review

Drug addiction is characterized by compulsive drug seeking and use, accompanied by negative emotional states (hyperkatifeia) and heightened pain sensitivity (hyperalgesia) during withdrawal. Both hyperalgesia and hyperkatifeia are integral components of substance use disorders, negatively impacting treatment and recovery. The underlying neurobiological mechanisms of hyperalgesia and hyperkatifeia involve alterations of brain reward and stress circuits, including the dynorphin/κ-opioid receptor (KOR) system. The dynorphin/KOR system modulates pain perception, negative affect, and addictive behaviors. Here, we review the preclinical evidence of dynorphin/KOR signaling in opioid withdrawal-induced hyperalgesia and hyperkatifeia.

Recent Findings

In opioid dependence models, pharmacological and genetic interventions of the dynorphin/KOR system attenuate somatic and motivational signs of withdrawal and addictive-like behaviors, highlighting its therapeutic potential. Understanding the intricate interplay between dynorphin/KOR signaling, hyperalgesia, hyperkatifeia, and addiction offers novel insights into treatment strategies for opioid use disorder and other substance use disorders.

Summary

Further research is needed to elucidate precise mechanisms of the sexual dimorphism of dynorphin/KOR signaling and identify targeted interventions to mitigate hyperalgesia and hyperkatifeia and facilitate recovery from addiction.

G Protein-Coupled Receptor Heteromers in Brain: Functional and Therapeutic Importance in Neuropsychiatric Disorders

G protein-coupled receptors (GPCRs) represent the largest family of plasma membrane proteins targeted for therapeutic development. For decades, GPCRs were investigated as monomeric entities during analysis of their pharmacology or signaling and during drug development. However, a considerable body of evidence now indicates that GPCRs function as dimers or higher-order oligomers. Greater acceptance of oligomerization occurred with the recognition that GPCR interactions form heteromeric receptor complexes, which was validated in vivo, often with pharmacologic, signaling, and functional properties distinct from the constituent protomers. GPCR heteromerization is reviewed in the context of brain disorders, with examples illustrating their functional implication in diverse neuropsychiatric and neurodegenerative disorders, making them an enormous unexploited resource for selective pharmacotherapy target identification. The strategies for development of heteromer-selective ligands are discussed as a new opportunity to precisely target the function of a receptor complex with greater specificity, in contrast to the classical ligands targeting individual receptors.

Endogenous opiates and behavior: 2023

This paper is the forty-sixth consecutive installment of the annual anthological review of research concerning the endogenous opioid system, summarizing articles published during 2023 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides and receptors as well as effects of opioid/opiate agonists and antagonists. The review is subdivided into the following specific topics: molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors (1), the roles of these opioid peptides and receptors in pain and analgesia in animals (2) and humans (3), opioid-sensitive and opioid-insensitive effects of nonopioid analgesics (4), opioid peptide and receptor involvement in tolerance and dependence (5), stress and social status (6), learning and memory (7), eating and drinking (8), drug and alcohol abuse (9), sexual activity and hormones, pregnancy, development and endocrinology (10), mental illness and mood (11), seizures and neurologic disorders (12), electrical-related activity and neurophysiology (13), general activity and locomotion (14), gastrointestinal, renal and hepatic functions (15), cardiovascular responses (16), respiration and thermoregulation (17), and immunological responses (18).

Tetrahydrocannabinol and dopamine D1 receptor

Dopamine is a hormone that is released by the adrenal gland and influences motor control and motivation. Dopamine is known to have 5 receptors which are D1, D2, D3, D4 and D5, which are further categorized into 2 families: D1 family and D2 family. The D1 family is known to play a role in motivation and motor control whereas the D2 family is known to affect attention and sleep. THC, a type of cannabinoid, can lead to feelings of euphoria, anxiety, fear, distrust, or panic. THC is known to affect dopamine in regions such as the anterior cingulate cortex (ACC), and plays a role in fundamental cognitive processes. Although there is a vast amount of research between the relationship of THC on dopamine, there continues to be limited research in relation to THC on dopamine receptors. The D1 receptor plays a role in several essential functions, such as memory, attention, impulse control, regulation of renal function, and locomotion. Accordingly, this review is intended to summarize the relationship between THC and D1 receptors, highlighting key gaps in the literature and avenues for future research.

Drug Interactions of Tetrahydrocannabinol and Cannabidiol in Cannabinoid Drugs

BACKGROUND

Cannabinoid drugs containing tetrahydrocannabinol (THC), or its structural analogues, as monotherapeutic agents or as extracts or botanical preparations with or without cannabidiol (CBD) are often prescribed to multimorbid patients who are taking multiple drugs. This raises the question of the risk of drug interactions.

METHODS

This review of the pharmacokinetics and pharmacodynamics of interactions with cannabinoid drugs and their potential effects is based on pertinent publications retrieved by a selective literature search.

RESULTS

As THC and CBD are largely metabolized in the liver, their bioavailability after oral or oral-mucosal administration is low (6-8% and 11-13%, respectively). The plasma concentrations of THC and its active metabolite 11-OH-THC can be increased by strong CYP3A4 inhibitors (verapamil, clarithromycin) and decreased by strong CYP3A4 inductors (rifampicin, carbamazepine). The clinical significance of these effects is unclear because of the variable plasma level and therapeutic spectrum of THC. The metabolism of CBD is less dependent on cytochrome P450 enzymes than that of THC. THC and CBD inhibit CYP2C and CYP3A4; the corresponding clinically relevant drug interactions probably are likely to arise only with THC doses above 30 mg/day and CBD doses above 300 mg/day.

CONCLUSION

Potential drug interactions with THC and CBD are probably of little importance at low or moderate doses. Strong CYP inhibitors or inductors can intensify or weaken their effect. Slowly ramping up the dose of oral cannabinoid drugs can lessen their pharmacodynamic interactions, which can generally be well controlled. Administration by inhalation can worsen the interactions.