Novel drugs for the treatment of chronic pruritus

Prurigo nodularis phenotype in the bullous dermatoses spectrum

Prurigo nodularis (PN) of Hyde is a highly pruritic condition that results from the vicious cycle of itching and scratching. An increasing number of case studies report PN-mimicking lesions in patients with confirmed autoimmune bullous dermatoses (AIBDs). The PN lesions usually precede the blister formation and thus raise the question about the pathogenic relation between the two conditions and the possible role of PN as a trigger of AIBDs. We shed light on PN in the context of AIBDs, especially regarding the clinical characteristics and pathogenesis of the PN-like phenotype of bullous pemphigoid, linear IgA bullous dermatosis, and dermatitis herpetiformis, as well as in the hereditary bullous dermatoses setting, namely, epidermolysis bullosa pruriginosa.

Chronic pruritus: from pathophysiology to drug design

Pruritus, the most common symptom in dermatology, is an innate response capable of protecting skin against irritants. Nonetheless, when it lasts more than six weeks it is assumed to be a chronic pathology having a negative impact on people's lives. Chronic pruritus (CP) can occur in common and rare skin diseases, having a high prevalence in global population. The existing therapies are unable to counteract CP or are associated with adverse effects, so the development of effective treatments is a pressing issue. The pathophysiological mechanisms underlying CP are not yet completely dissected but, based on current knowledge, involve a wide range of receptors, namely neurokinin 1 receptor (NK1R), Janus kinase (JAK), and transient receptor potential (TRP) ion channels, especially transient receptor potential vanilloid 1 (TRPV1) and transient receptor potential ankyrin 1 (TRPA1). This review will address the relevance of these molecular targets for the treatment of CP and molecules capable of modulating these receptors that have already been studied clinically or have the potential to possibly alleviate this pathology. According to scientific and clinical literature, there is an increase in the expression of these molecular targets in the lesioned skin of patients experiencing CP when compared with non-lesioned skin, highlighting their importance for the development of potential efficacious drugs through the design of antagonists/inhibitors.

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.

Molecular Genetics of Kappa Opioids in Pain and Itch Sensations

The opioid peptides and their receptors have been linked to multiple key biological processes in the nervous system. Here we review the functions of the kappa opioid receptor (KOR) and its endogenous agonists dynorphins (Goldstein A, Tachibana S, Lowney LI, Hunkapiller M, Hood L, Proc Natl Acad Sci U S A 76:6666-6670, 1979) in modulating itch and pain (nociception). Specifically, we discuss their roles relative to recent findings that tell us more about the cells and circuits which are impacted by this opioid and its receptor and present reanalysis of single-cell sequencing data showing the expression profiles of these molecules. Since the KOR is relatively specifically activated by peptides derived from the prodynorphin gene and other opioid peptides that show lower affinities, this will be the only interactions we consider (Chavkin C, Goldstein A, Nature 291:591-593, 1981; Chavkin C, James IF, Goldstein A, Science 215:413-415, 1982), although it was noted that at higher doses peptides other than dynorphins might stimulate KOR (Lai J, Luo MC, Chen Q, Ma S, Gardell LR, Ossipov MH, Porreca F, Nat Neurosci 9:1534-1540, 2006). This review has been organized based on anatomy with each section describing the effect of the kappa opioid system in a specific location but let us not forget that most of these circuits are interconnected and are therefore interdependent.

Electrically Evoked Itch in Human Subjects

Administration of chemicals (pruritogens) into the skin evokes itch based on signal transduction mechanisms that generate action potentials mainly in mechanically sensitive and insensitive primary afferent C-fibers (pruriceptors). These signals from peripheral neurons are processed in spinal and supra-spinal centers of the central nervous system and finally generate the sensation of itch. Compared to chemical stimulation, electrical activation of pruriceptors would allow for better temporal control and thereby a more direct functional assessment of their activation. Here, we review the electrical stimulation paradigms which were used to evoke itch in humans in the past. We further evaluate recent attempts to explore electrically induced itch in atopic dermatitis patients. Possible mechanisms underlying successful pruritus generation in chronic itch patients by transdermal slowly depolarizing electrical stimulation are discussed.

Inpatient Management of Mucocutaneous GVHD

Purpose of Review

Graft-versus-host disease (GVHD) is an immune mediated disorder affecting 30 - 70% of patients after allogeneic hematopoietic stem cell transplantation (alloHSCT), and is a major cause of morbidity and non-relapse mortality (NRM) [1]. Dermatologists play a critical role in acute and chronic GVHD, as skin involvement is common and often the earliest involved site of disease [2].

Recent Findings

GVHD shares clinical and histopathological features with a variety of other skin diseases, requiring thorough consideration of differential diagnoses in hematopoietic stem cell transplantation (HSCT) recipients with lesions suggestive of cutaneous GVHD. Treatment considerations for GVHD are influenced by factors such as disease classification, overall grading, organ involvement, associated symptoms, and immunological anti-tumor effect. Several treatments are available and may be indicated as monotherapy or adjuvant therapy to allow faster withdrawal or tapering of immunosuppression. While corticosteroids are often first line therapy, oral ruxolitinib has been recently approved for treatment of steroid-refractory aGHVD, and oral ibrutinib has been approved for steroid-refractory cGHVD.

Summary

This article provides current clinical, diagnostic, and therapeutic considerations relevant to the hospitalist for both acute and chronic mucocutaneous GVHD. Optimal inpatient management of these diseases requires an interdisciplinary team.

Pathophysiology, diagnosis, and pharmacological treatment of prurigo nodularis

Introduction: Prurigo nodularis (PN) is a chronic inflammatory skin disease characterized by intensely pruritic, hyperkeratotic nodules distributed on the trunk and extensor surfaces of the extremities. PN has a profoundly negative impact on sleep and quality of life in patients with PN. There are currently no U.S. Food and Drug Administration-approved agents and patients are often recalcitrant to current therapies, highlighting the importance of further research into this severely debilitating condition. Areas covered: A PubMed search was conducted to find available literature on the pathophysiology and clinical management of PN. In this review article, we discuss the current understanding of the pathophysiology, recommended diagnostic approach, and treatment options available for PN. Expert opinion/commentary: PN is an extremely difficult condition to treat, because there is a lack of effective therapies available due to our limited understanding of its pathophysiology. Currently, available treatment options are often multimodal due to the intersection of neuroimmune etiologic factors in the pathogenesis of PN. Fortunately, as our knowledge of PN expands, novel treatments targeting specific molecular biomarkers of PN are emerging, providing hope to this long-suffering patient population.

The Neurokinin-1 Receptor is Expressed with Gastrin-Releasing Peptide Receptor in Spinal Interneurons and Modulates Itch

The neurokinin-1 receptor (NK1R; encoded by Tacr1) is expressed in spinal dorsal horn neurons and has been suggested to mediate itch in rodents. However, previous studies relied heavily on neurotoxic ablation of NK1R spinal neurons, which limited further dissection of their function in spinal itch circuitry. To address this limitation, we leveraged a newly developed Tacr1CreER mouse line to characterize the role of NK1R spinal neurons in itch. We show that pharmacological activation of spinal NK1R and chemogenetic activation of Tacr1CreER spinal neurons increases itch behavior in male and female mice, whereas pharmacological inhibition of spinal NK1R suppresses itch behavior. We use fluorescence in situ hybridization (FISH) to characterize the endogenous expression of Tacr1 throughout the superficial and deeper dorsal horn (DDH), as well as the lateral spinal nucleus (LSN), of mouse and human spinal cord. Retrograde labeling studies in mice from the parabrachial nucleus (PBN) show that less than 20% of superficial Tacr1CreER dorsal horn neurons are spinal projection neurons, and thus the majority of Tacr1CreER are local interneurons. We then use a combination of in situ hybridization and ex vivo two-photon Ca2+ imaging of the mouse spinal cord to establish that NK1R and the gastrin-releasing peptide receptor (GRPR) are coexpressed within a subpopulation of excitatory superficial dorsal horn (SDH) neurons. These findings are the first to suggest a role for NK1R interneurons in itch and extend our understanding of the complexities of spinal itch circuitry.SIGNIFICANCE STATEMENT The spinal cord is a critical hub for processing somatosensory input, yet which spinal neurons process itch input and how itch signals are encoded within the spinal cord is not fully understood. We demonstrate neurokinin-1 receptor (NK1R) spinal neurons mediate itch behavior in mice and that the majority of NK1R spinal neurons are local interneurons. These NK1R neurons comprise a subset of gastrin-releasing peptide receptor (GRPR) interneurons and are thus positioned at the center of spinal itch transmission. We show NK1R mRNA expression in human spinal cord, underscoring the translational relevance of our findings in mice. This work is the first to suggest a role for NK1R interneurons in itch and extends our understanding of the complexities of spinal itch circuitry.

Practical approaches for diagnosis and management of prurigo nodularis: United States expert panel consensus

BACKGROUND

Prurigo nodularis (PN) is a chronic disease characterized by intensely pruritic, raised, nodular lesions. Because there are currently no United States Food and Drug Administration-approved therapies specifically for PN, management is highly variable, and no consensus exists on treatment regimens.

OBJECTIVE

To provide practical guidance to help United States dermatologists diagnose and effectively treat patients with PN.

METHODS

We participated in a roundtable discussion to develop consensus recommendations on diagnosis and treatment of PN from a United States perspective.

RESULTS

The core findings in PN are the presence of firm, nodular lesions; pruritus lasting at least 6 weeks; and a history or signs, or both, of repeated scratching, picking, or rubbing. The diagnostic workup involves a complete review of systems, considering potential systemic diseases, and assessment of disease severity, including disease burden and pruritus intensity. Treatment should be selected based on a patient's clinical presentation, comorbidities, and response to prior treatments and should address both neural and immunologic components of pruritus.

LIMITATIONS

Data on PN are from anecdotal or small clinical trials, and all treatments are currently used off-label.

CONCLUSION

An effective treatment approach for patients with PN should be based on clinical judgment and tailored to the individual needs of the patient.

Prurigo nodularis: Pathogenesis and management

Prurigo nodularis is a chronic skin condition characterized by severely pruritic nodules that cause a profound negative impact on quality of life. The second article in this 2-part continuing medical education series focuses on reviewing the pathogenesis of prurigo nodularis and exploring management algorithms for this condition. In addition, we discuss some emerging and novel therapies for treating prurigo nodularis. The first article in this 2-part series describes the broader epidemiology, patient demographics, physical examination findings, and symptoms to aid in the timely recognition and diagnosis of prurigo nodularis.

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.