Gabapentin and pregabalin inhibit the itch-associated response induced by the repeated application of oxazolone in mice

Mirogabalin inhibits scratching behavior of spontaneous model mouse of atopic dermatitis

Introduction: Atopic dermatitis (AD) is one of the most prevalent intractable chronic itch diseases worldwide. In recent years, new molecular-targeted drugs have emerged, but side effects and economic challenges remain. Therefore, since it is important for AD patients to have a wider range of treatment options, it is important to explore new therapeutic agents. Gabapentinoids, gabapentin and pregabalin, have been shown to be effective for the clinical treatment of several chronic itch. Recently, mirogabalin (MGB) was developed as a novel gabapentinoid. MGB is a drug for neuropathic pain and has a margin of safety between its side effects and the analgesic effect for animal experiments. Herein, we showed that MGB exhibited an antipruritic effect in a mouse model of AD using NC/Nga mice. Methods and results: The oral administration of MGB (10 mg/kg) inhibited spontaneous scratching behavior in AD mice and its effect was dose dependently. Then, when MGB (10 mg/kg) was orally administrated to healthy mice, it did not affect motor function, including locomotor activity, wheel activity, and coordinated movement. Moreover, gabapentin (100 mg/kg) and pregabalin (30 mg/kg), inhibited spontaneous scratching behavior in AD mice and decreased motor function in healthy mice. Furthermore, intracisternal injection of MGB (10 μg/site) significantly suppressed spontaneous scratching behavior in AD mice. Discussion: In summary, our results suggest that MGB exerts an antipruritic effect via the spinal dorsal horn using NC/Nga mice. We hope that MGB is a candidate for a novel therapeutic agent for AD with relatively few side effects.

Model of Chronic Itch in Aged Mice: Beneficial Effects of Drugs Affecting Descending Modulatory Systems

Pruritus in the elderly, particularly those cases without skin dryness or other identifiable causes, makes treatment challenging due to the lack of evidence regarding the therapeutic effects of antipruritics. This study proposes an age-related alloknesis mouse model for an evaluation system for such cases, and aimed to investigate the effectiveness and mechanisms of action of several drugs commonly used as antipruritics in Japan, utilizing this model. Mice 69-80 weeks old were used as aged mice, and the level of mechanical alloknesis was counted as the number of scratching behaviours in response to innocuous stimuli. Bepotastine, neurotropin, pregabalin, baricitinib, and abrocitinib were used as antipruritics, and yohimbine and methysergide as inhibitors of the descending inhibitory pathway. The findings suggest that mechanical alloknesis in aged mice is a suitable animal model for assessing pruritus in the elderly without xerosis, and pregabalin, neurotropin, baricitinib, and abrocitinib may be effective antipruritics in the elderly through activating both the noradrenergic and serotonergic descending inhibitory pathways. These findings may be useful for the selection of antipruritics for pruritus in the elderly without skin lesions or dryness.

[Neuropathic pruritus-Evidence-based treatment recommendations]

Neuropathic pruritus is a previously neglected symptom of a wide range of neurological diseases. Peripheral nerve or root compression syndromes, space-occupying lesions of the central nervous system, chronic inflammatory neurological diseases and polyneuropathy can cause neuropathic pruritus. Even when the identification of the underlying neurological disease is successful, a direct causal treatment is not always possible, hence an effective symptomatic treatment remains the only therapeutic option. The purpose of this review article is to present the current literature on various therapeutic agents and options in the treatment of neuropathic pruritus.

Comparative Study on Different Skin Pruritus Mouse Models

The animal model is an important tool to study the mechanism of disease formation. Different animal models of pruritus have been adopted based on the purpose of researchers in the study of the itching mechanism. Although the symptoms of various models are quite different, scratching behavior is a key indicator. Therefore, it is necessary to find an animal model that can quickly induce animal scratching and maintain the stability of scratching behavior. In this study, we compared animal models of pruritus induced by four substances and found that the scratching behavior of mice induced by urushiol not only reached the plateau stage quickly but also showed more stability in the plateau phase than that induced by 2,4-dinitrofluorobenzene, oxazolone, and imiquimod. Meanwhile, in the animal model induced by urushiol, the changes of epidermal thickening and inflammatory cell aggregation were also more obvious. In addition, pruritus induced by urushiol is prevalent all over the world, especially in the United States and Europe, involving outdoor groups such as firefighters, forest loggers, and farmers. Therefore, we believe that the urushiol-induced animal model is an ideal choice for the study of the itch formation mechanism and the development of antipruritic drugs.

Noradrenergic modulation of itch transmission in the spinal cord

Inhibition of both itching and scratching is important in the treatment of chronic pruritic diseases, because itching has a negative impact on quality of life and vigorous scratching worsens skin conditions. Pharmacological modulation of itch transmission in the dorsal horn is an effective way to inhibit both itching and scratching in pruritic diseases. Pruriceptive transmission in the spinal dorsal horn undergoes inhibitory modulation by the descending noradrenergic system. The noradrenergic inhibition is mediated by excitatory α₁-adrenoceptors located on inhibitory interneurons and inhibitory α₂-adrenoceptors located on central terminals of primary sensory neurons. The descending noradrenergic system and α-adrenoceptors in the dorsal horn are potential targets for antipruritic drugs.

An aberrant parasympathetic response: a new perspective linking chronic stress and itch

Perceived stress has long been known to alter the dynamic equilibrium established between the nervous, endocrine and immune system and is widely recognised to trigger or enhance pruritus. However, the exact mechanism of how the major stress response systems, such as the hypothalamus-pituitary adrenal (HPA) axis and the autonomic nervous system induce or aggravate chronic itch, has not been elucidated. The limbic regions of the brain such as the prefrontal cortex and hippocampus are deeply involved in the regulation of the stress response and intersect with circuits that are responsible for memory and reward. According to the 'Polyvagal Theory', certain limbic structures that serve as a 'higher brain equivalent of the parasympathetic nervous system' play a foremost role in maintaining body homoeostasis by functioning as an active vagal brake. In addition, the limbic system has been postulated to regulate two distinct, yet related aspects of itch: (i) the sensory-discriminative aspect; and (ii) the affective-cognitive aspect. Chronic stress-induced itch is hypothesised to be caused by stress-related changes in limbic structure with subsequent rewiring of both the peripheral and central pruriceptive circuits. Herein, we review data suggesting that a dysfunctional parasympathetic nervous system associated with chronic stress may play a critical role in the regulatory control of key candidate molecules, receptors and brain structures involved in chronic itch.

Treatment of prurigo nodularis with pregabalin

WHAT IS KNOWN AND OBJECTIVE

Prurigo nodularis (PN) is a chronic skin condition that is difficult to treat. Pregabalin is one of the possible treatments for PN but its safety and efficacy are not well defined. We aimed to assess the efficacy of pregabalin in patients with PN.

METHODS

Thirty patients (10 men, 20 women; mean age 51.6 ± 9.39 years) were treated with pregabalin (75 mg/day) for 3 months. Efficacy was classified as (i) successful (disappearance of the pruritus and reduction of nodules); (ii) slight improvement/reduction of the nodules, that is, number and/or flattening, no disappearance of itching; or (iii) unsuccessful.

RESULTS

Twenty-three patients (76%) responded successfully after 3 months of treatment. There was a statistically significant difference between visual analogue scale scores before and after 1 month treatment period (8·15 ± 2·04 and 1·5 ± 1·12, respectively; P < 0·0001). Pregabalin was generally well tolerated with only six (20%) patients reporting side effects. No patient showed any renal insufficiency.

WHAT IS NEW AND CONCLUSION

In our study, pregabalin was effective for the treatment of PN. However, given the open and non-controlled study design used, a properly powered randomized controlled validation study is called for.