Involvement of spinal cannabinoid receptors in the antipruritic effects of WIN 55,212-2, a cannabinoid receptor agonist

The synthetic cannabinoid agonist WIN 55,212-2 reduces experimental pruritus via CB2 receptor activation

Pruritus (i.e., the experience that evokes a desire to scratch) is an adaptive process that can become maladaptive, leading to a persistent scratch-itch cycle that potentiates pruritus and increases the risk of infection. Cannabinoid drugs have been reported to decrease pruritus, but often at doses that also decrease locomotor activity, which confounds assessments of utility. To determine the utility of cannabinoids in treating pruritus without undesirable adverse effects, the current preclinical study investigated a range of doses of the synthetic cannabinoid agonist, WIN 55,212-2, and two minor Cannabis phytoconstituents, Δ8-tetrahydrocannabinol and β-caryophyllene, in experimentally induced pruritus in male and female C57BL/6J adult mice. WIN 55,212-2 reduced compound 48/80-induced scratching, and this antipruritic effect was prevented by either chemically blocking (via SR144528 antagonism) or genetically deleting the CB2 cannabinoid receptor. The CB2 receptor selective agonist, JWH-133, also attenuated compound 48/80-induced scratching, while the CB1 positive allosteric modulator, ZCZ011, had no effect. Similarly, the minor phytocannabinoid Δ8-tetrahydrocannabinol reduced scratching at doses that did not affect locomotor activity. In contrast, the sesquiterpene cannabis constituent β-caryophyllene induced scratching, acting as a pruritogen. These preclinical data support the continuing investigation of cannabinoid receptor modulation as a potential therapeutic strategy for pruritus.

Differential regulation of pruritic sensation and emotion by cannabinoid type 1 receptors on mPFC glutamatergic and GABAergic neurons

Itch causes a strong urge to scratch and induces negative emotions, such as aversion and anxiety. Antihistamine medications are key in the clinical management of pruritus, but their therapeutic efficacy in controlling moderate and severe itching remains limited. The neural circuits in the brain that process itching and itch-induced aversion and anxiety remain unclear so far. Human brain imaging suggests that the medial prefrontal cortex (mPFC) is involved in processing the emotional and motivational components of itching. In this study, we investigated the mechanisms by which glutamatergic and GABAergic neurons in mPFC differentially regulated pruritic sensation and emotion through cannabinoid type 1 receptors (CB1Rs). Chloroquinoline (CQ)-induced acute and calcipotriol (MC903)-induced chronic itch models were established. Fiberoptic calcium imaging was used to detect the activity of the two types of neurons in response to itching. The CB1R antagonist AM251 (0.5 mg in 200 nL) was microinjected into the mPFC through the implanted cannula. We showed that chemogenetic activation of glutamatergic neurons and inhibition of GABAergic neurons in the mPFC reduced scratching and chronic itch-induced anxiety. GABAergic, but not glutamatergic, neurons were involved in acute itch-induced aversion. CB1Rs on glutamatergic and GABAergic neurons modulated chronic itch-induced scratching and anxiety in divergent manners. However, CB1Rs did not affect acute itch-induced scratching. CB1Rs on GABAergic, but not glutamatergic, neurons regulated acute itch-induced aversion. These results may guide the development of therapeutic strategies targeting CB1Rs to treat itch-induced sensory and emotional responses.

Cannabinoids and Their Receptors in Skin Diseases

The therapeutic application of cannabinoids has gained traction in recent years. Cannabinoids interact with the human endocannabinoid system in the skin. A large body of research indicates that cannabinoids could hold promise for the treatment of eczema, psoriasis, acne, pruritus, hair disorders, and skin cancer. However, most of the available data are at the preclinical stage. Comprehensive, large-scale, randomized, controlled clinical trials have not yet been fully conducted. In this article, we describe new findings in cannabinoid research and point out promising future research areas.

Cannabis and cannabinoids in dermatology: protocol for a systematic review and meta-analysis of quantitative outcomes

INTRODUCTION

Following the discovery of various effects on skin function by modifying endocannabinoid systems, multiple preclinical studies have revealed the promise of cannabis and cannabinoids in the treatment of a variety of skin diseases. However, its clinical efficacy is still debated.

METHODS AND ANALYSIS

The protocol has been prepared using the Preferred Items for Systematic Review and Meta-analysis Protocols guidelines. A systematic search will be conducted using PubMed, EMBASE, SCOPUS, the Cochrane Central Register of Controlled Trials and Web of Science. We will include randomised controlled trials and observational studies investigating alterations to dermatological characteristics following administration of cannabis and cannabinoids for dermatological diseases and disorders. The two reviewers will perform both the title and abstract and full-text screenings. The Cochrane Risk-of-Bias 2 and ROBINS-1 tools will be used to evaluate the risk of bias. If a group of comparable studies for each quantitative outcome can be discovered, we will conduct a random effects meta-analysis. We will investigate heterogeneity using a combination of visual inspection of the forest plot, the Cochran's Q test and Higgins' test [I2]. Sensitivity analyses will be performed to assess the statistical robustness of the primary outcome. To evaluate a publication bias, the Egger's regression asymmetry test and funnel plots will be considered.

ETHICS AND DISSEMINATION

This study does not require ethical approval because no original data will be collected. The findings will be presented at conferences and published in peer-reviewed journals.

PROSPERO REGISTRATION NUMBER

CRD42023397189.

How to get rid of itching

Itch is an unpleasant sensation arising from a variety of dermatologic, neuropathic, systemic, and psychogenic etiologies. Various itch pathways are implicated according to the underlying etiology. A variety of pruritogens, or itch mediators, as well as receptors have been identified and provide potential therapeutic targets. Recent research has primarily focused on targeting inflammatory cytokines and Janus kinase signaling, protease-activated receptors, substance P and neurokinin, transient receptor potential-vanilloid ion channels, Mas-related G-protein-coupled receptors (MRGPRX2 and MRGPRX4), the endogenous opioid and cannabinoid balance, and phosphodiesterase 4. Periostin, a newly identified pruritogen, should be further explored with clinical trials. Drugs targeting neural sensitization including the gabergic system and P2X3 are other potential drugs for chronic itch. There is a need for more targeted therapies to improve clinical outcomes and reduce side effects.

Electroacupuncture reduces chronic itch via cannabinoid CB1 receptors in the ventrolateral periaqueductal gray

Chronic itch severely reduces the quality of life of patients. Electroacupuncture (EA) is widely used to treat chronic itch. However, the underlying mechanism of this therapeutic action of EA is largely unknown. Cannabinoid CB1 receptors in the ventrolateral periaqueductal gray (vlPAG) mediate the analgesic effect of EA. Using a dry skin-induced itch model in mice, we determined whether EA treatment reduces chronic itch via CB1 receptors in the vlPAG. We showed that the optimal inhibitory effect of EA on chronic itch was achieved at the high frequency and high intensity (100 Hz and 3 mA) at “Quchi” (LI11) and “Hegu” (LI14) acupoints, which are located in the same spinal dermatome as the cervical skin lesions. EA reversed the increased expression of CB1 receptors in the vlPAG and decreased the concentration of 5-hydroxytryptamine (5-HT) in the medulla oblongata and the expression of gastrin-releasing peptide receptors (GRPR) in the cervical spinal cord. Furthermore, knockout of CB1 receptors on GABAergic neurons in the vlPAG attenuated scratching behavior and the 5-HT concentration in the medulla oblongata. In contrast, knockout of CB1 receptors on glutamatergic neurons in the vlPAG blocked the antipruritic effects of EA and the inhibitory effect of EA on the 5-HT concentration in the medulla oblongata. Our findings suggest that EA treatment reduces chronic itch by activation of CB1 receptors on glutamatergic neurons and inhibition of CB1 receptors on GABAergic neurons in the vlPAG, thereby inhibiting the 5-HT release from the medulla oblongata to GRPR-expressing neurons in the spinal cord. Our findings suggest that EA attenuates chronic itch via activating CB1 receptors expressed on glutamatergic neurons and downregulating CB1 receptors on GABAergic neurons in the vlPAG, leading to the reduction in 5-HT release in the rostroventral medulla and GRPR signaling in the spinal cord. Our study not only advances our understanding of the mechanisms of the therapeutic effect of EA on chronic itch but also guides the selection of optimal parameters and acupoints of EA for treating chronic itch.

Druggable Targets and Compounds with Both Antinociceptive and Antipruritic Effects

Pain and itch are both important manifestations of various disorders, such as herpes zoster, atopic dermatitis, and psoriasis. Growing evidence suggests that both sensations have shared mediators, overlapping neural circuitry, and similarities in sensitization processes. In fact, pain and itch coexist in some disorders. Determining pharmaceutical agents and targets for treating pain and itch concurrently is of scientific and clinical relevance. Here we review the neurobiology of pain and itch and discuss the pharmaceutical targets as well as novel compounds effective for the concurrent treatment of these sensations.

Peripherally administered cannabinoid receptor 2 (CB2R) agonists lose anti-allodynic effects in TRPV1 knockout mice, while intrathecal administration leads to anti-allodynia and reduced GFAP, CCL2 and TRPV1 expression in the dorsal spinal cord and DRG

The transient receptor potential (TRP) superfamily of cation channels, of which the TRP vanilloid type 1 (TRPV1) receptor plays a critical role in inflammatory and neuropathic pain, is expressed on nociceptors and spinal cord dorsal horn neurons. TRPV1 is also expressed on spinal astrocytes and dorsal root ganglia (DRG) satellite cells. Agonists of the cannabinoid type 2 receptor (CB2R) suppress allodynia, with some that can bind TRPV1. The neuroimmune C-C class chemokine-2 (CCL2) expressed on injured DRG nociceptor cell bodies, Schwann cells and spinal astrocytes, stimulates immune cell accumulation in DRG and spinal cord, a known critical element in chronic allodynia. The current report examined whether two CB2R agonists, AM1710 and AM1241, previously shown to reverse light touch mechanical allodynia in rodent models of sciatic neuropathy, require TRPV1 activation that leads to receptor insensitivity resulting in reversal of allodynia. Global TRPV1 knockout (KO) mice with sciatic neuropathy given intrathecal or intraperitoneal AM1710 were examined for anti-allodynia followed by immunofluorescent microscopy analysis of lumbar spinal cord and DRG of astrocyte and CCL2 markers. Additionally, immunofluorescent analysis following intrathecal AM1710 and AM1241 in rat was performed. Data reveal that intrathecal AM1710 resulted in mouse anti-allodynia, reduced spinal astrocyte activation and CCL2 expression independent of TRPV1 gene deletion. Conversely, peripheral AM1710 in TRPV1-KO mice failed to reverse allodynia. In rat, intrathecal AM1710 and AM1241 reduced spinal and DRG TRPV1 expression, with CCL2-astrocyte and -microglial co-expression. These data support that CB2R agonists can impact spinal and DRG TRPV1 expression critical for anti-allodynia.

Cannabis and the skin

The public and health care providers are increasingly curious about the potential medical benefits of Cannabis. In vitro and in vivo studies of Cannabis have suggested it has favorable effects on regulating pain, pruritus, and inflammation, making it a potentially attractive therapeutic agent for many dermatologic conditions. The body of literature reporting on the role of cannabinoids in dermatology is in its infancy but growing. We review the current research, possible cutaneous adverse effects, and future directions for cannabinoids and their use in skin cancer, acne, psoriasis, pruritus, dermatitis, scleroderma, dermatomyositis, cutaneous lupus erythematous, epidermolysis bullosa, pain, and wound healing.

Therapeutic Potential of Cannabidiol (CBD) for Skin Health and Disorders

Though there is limited research confirming the purported topical benefits of cannabinoids, it is certain that cutaneous biology is modulated by the human endocannabinoid system (ECS). Receptors from the ECS have been identified in the skin and systemic abuse of synthetic cannabinoids, and their analogs, have also been associated with the manifestation of dermatological disorders, indicating the effects of the ECS on cutaneous biology. In particular, cannabidiol (CBD), a non-psychoactive compound from the cannabis plant, has garnered significant attention in recent years for its anecdotal therapeutic potential for various pathologies, including skin and cosmetic disorders. Though a body of preclinical evidence suggests topical application of CBD may be efficacious for some skin disorders, such as eczema, psoriasis, pruritis, and inflammatory conditions, confirmed clinical efficacy and elucidation of underlying molecular mechanisms have yet to be fully identified. This article provides an update on the advances in CBD research to date and the potential areas of future exploration.

Cannabinoids for the treatment of chronic pruritus: A review

Medical marijuana is becoming widely available to patients in the United States, and with recreational marijuana now legalized in many states, patient interest is on the rise. The endocannabinoid system plays an important role in skin homeostasis in addition to broader effects on neurogenic responses such as pruritus and nociception, inflammation, and immune reactions. Numerous studies of in vitro and animal models have provided insight into the possible mechanisms of cannabinoid modulation on pruritus, with the most evidence behind neuronal modulation of peripheral itch fibers and centrally acting cannabinoid receptors. In addition, human studies, although limited due to differences in the cannabinoids used, disease models, and delivery method, have consistently shown significant reductions in both scratching and symptoms in chronic pruritus. Clinical studies have shown a reduction in pruritus in several dermatologic (atopic dermatitis, psoriasis, asteatotic eczema, prurigo nodularis, and allergic contact dermatitis) and systemic (uremic pruritus and cholestatic pruritus) diseases. These preliminary human studies warrant controlled trials to confirm the benefit of cannabinoids for treatment of pruritus and to standardize treatment regimens and indications. In patients who have refractory chronic pruritus after standard therapies, cannabinoid formulations may be considered as an adjuvant therapy where it is legal.

Neuroimmune interactions in chronic itch of atopic dermatitis

Itch is a defining symptom of atopic dermatitis. Crosstalk between keratinocytes, the immune system and non‐histaminergic sensory nerves is responsible for the pathophysiology of chronic itch in atopic dermatitis. An expanding understanding of the contribution of the nervous system and its interaction with immune pathways in atopic itch are helping to identify new therapeutic strategies.

Itch: From mechanism to (novel) therapeutic approaches

Itch is a common sensory experience that is prevalent in patients with inflammatory skin diseases, as well as in those with systemic and neuropathic conditions. In patients with these conditions, itch is often severe and significantly affects quality of life. Itch is encoded by 2 major neuronal pathways: histaminergic (in acute itch) and nonhistaminergic (in chronic itch). In the majority of cases, crosstalk existing between keratinocytes, the immune system, and nonhistaminergic sensory nerves is responsible for the pathophysiology of chronic itch. This review provides an overview of the current understanding of the molecular, neural, and immune mechanisms of itch: beginning in the skin, proceeding to the spinal cord, and eventually ascending to the brain, where itch is processed. A growing understanding of the mechanisms of chronic itch is expanding, as is our pipeline of more targeted topical and systemic therapies. Our therapeutic armamentarium for treating chronic itch has expanded in the last 5 years, with developments of topical and systemic treatments targeting the neural and immune systems.

The Neuromodulatory Effect of Antipruritic Treatment of Chronic Prurigo

Chronic prurigo is an extremely severe pruritic skin disease which presents with multiple, hyperkeratotic and erosive papules, nodules and/or plaques. Patients with this high-burden disease require effective therapies, but effective treatments with regulatory agency approval are currently lacking. Deeper understanding of the pathophysiology suggests that hypersensitive nerves play an important role in the development of chronic prurigo. Accordingly, a treatment with neuroactive substances which modulate hypersensitivity seems promising. Here, we review antipruritic therapies with a neuromodulative effect. Current treatment options, such as topical capsaicin or opioid-receptor modulators, and also novel and future treatment regimens, such as, for example, interleukin-31 antibodies and neurokinin-1 receptor antagonists, are discussed.

Cannabinoid Signaling in the Skin: Therapeutic Potential of the "C(ut)annabinoid" System

The endocannabinoid system (ECS) has lately been proven to be an important, multifaceted homeostatic regulator, which influences a wide-variety of physiological processes all over the body. Its members, the endocannabinoids (eCBs; e.g., anandamide), the eCB-responsive receptors (e.g., CB₁, CB₂), as well as the complex enzyme and transporter apparatus involved in the metabolism of the ligands were shown to be expressed in several tissues, including the skin. Although the best studied functions over the ECS are related to the central nervous system and to immune processes, experimental efforts over the last two decades have unambiguously confirmed that cutaneous cannabinoid ("c[ut]annabinoid") signaling is deeply involved in the maintenance of skin homeostasis, barrier formation and regeneration, and its dysregulation was implicated to contribute to several highly prevalent diseases and disorders, e.g., atopic dermatitis, psoriasis, scleroderma, acne, hair growth and pigmentation disorders, keratin diseases, various tumors, and itch. The current review aims to give an overview of the available skin-relevant endo- and phytocannabinoid literature with a special emphasis on the putative translational potential, and to highlight promising future research directions as well as existing challenges.