Benefits and harms of NK1 R antagonists in pruritus: A systematic review and meta-analysis

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.

Inhibition of itch by neurokinin 1 receptor (Tacr1) -expressing ON cells in the rostral ventromedial medulla in mice

The rostral ventromedial medulla (RVM) is important in descending modulation of spinal nociceptive transmission, but it is unclear if the RVM also modulates spinal pruriceptive transmission. RVM ON cells are activated by noxious algesic and pruritic stimuli and are pronociceptive. Many RVM-spinal projection neurons express the neurokinin-1 receptor (Tacr1), and ON-cells are excited by local administration of substance P (SP). We hypothesized that Tacr1-expressing RVM ON cells exert an inhibitory effect on itch opposite to their pronociceptive action. Intramedullary microinjection of SP significantly potentiated RVM ON cells and reduced pruritogen-evoked scratching while producing mild mechanical sensitization. Chemogenetic activation of RVM Tacr1-expressing RVM neurons also reduced acute pruritogen-evoked scratching. Optotagging experiments confirmed RVM Tacr1-expressing neurons to be ON cells. We conclude that Tacr1-expressing ON cells in RVM play a significant role in the modulation of pruriceptive transmission.

Non-Atopic Chronic Nodular Prurigo (Prurigo Nodularis Hyde): A Systematic Review of Best-Evidenced Treatment Options

BACKGROUND

Chronic nodular prurigo (CNPG) is a chronic, inflammatory skin disease, characterized by intense and debilitating pruritus. The pathophysiology is not fully understood, and the condition is difficult to treat with no targeted therapies. The aim of this systematic review was to review the evidence of therapies for non-atopic CNPG and conduct a meta-analysis of the results.

SUMMARY

We conducted a systematic review of the literature concerning effect of treatment for non-atopic CNPG. Due to few randomized controlled trials (RCTs) and case series, the literature was unfortunately too sparse to conduct a meta-analysis of the results. Instead, we thoroughly report important data from the three existing RCTs and 6 case studies with more than 15 patients. Evaluated therapies include nemolizumab, aprepitant, topical therapy with hydrocortisone and pimecrolimus, thalidomide, UVA phototherapy, pregabalin, and naltrexone. Included RCTs and case studies all had a heterogeneous methodology making direct comparison almost impossible.

KEY MESSAGES

There is sparse evidence for the currently used therapies for non-atopic CNPG. Several RCTs on new therapies are running or in the pipeline, hopefully providing new, effective, and targeted treatment possibilities for CNPG patients both with and without an atopic predisposition.