Repeated application of glucocorticoids exacerbate pruritus via inhibition of prostaglandin D2 production of mast cells in a murine model of allergic contact dermatitis

Satellite Glial Cells and Neurons in Trigeminal Ganglia Are Altered in an Itch Model in Mice

Itch (pruritus) is a common chronic condition with a lifetime prevalence of over 20%. The mechanisms underlying itch are poorly understood, and its therapy is difficult. There is recent evidence that following nerve injury or inflammation, intercellular communications in sensory ganglia are augmented, which may lead to abnormal neuronal activity, and hence to pain, but there is no information whether such changes take place in an itch model. We studied changes in neurons and satellite glial cells (SGCs) in trigeminal ganglia in an itch model in mice using repeated applications of 2,4,6-trinitro-1-chlorobenzene (TNCB) to the external ear over a period of 11 days. Treated mice showed augmented scratching behavior as compared with controls during the application period and for several days afterwards. Immunostaining for the activation marker glial fibrillary acidic protein in SGCs was greater by about 35% after TNCB application, and gap junction-mediated coupling between neurons increased from about 2% to 13%. The injection of gap junction blockers reduced scratching behavior, suggesting that gap junctions contribute to itch. Calcium imaging studies showed increased responses of SGCs to the pain (and presumed itch) mediator ATP. We conclude that changes in both neurons and SGCs in sensory ganglia may play a role in itch.

Casearia decandra leaves present anti-inflammatory efficacy in a skin inflammation model in mice

ETHNOPHARMACOLOGICAL RELEVANCE

Casearia decandra (guaçatonga) is popularly used as an anti-inflammatory. We investigated the antioxidant and anti-inflammatory effect of C.decandra leaves (CdE) ethanolic extract and of the rutin standard (present in the CdE).

MATERIALS AND METHODS

Male adult Swiss mice were used (25-30 g; 5-6 animals by a group). CdE phytochemical analysis was performed by HPLC method. The antioxidant potential of CdE and rutin was assessed by different methods. Topical anti-inflammatory effect of CdE (0.001-1mg/ear) and rutin (0.003-0.03mg/ear) was evaluated by ear edema formation and inflammatory cells infiltration (MPO activity and histology) on a skin inflammation model induced by topical application of croton oil (1mg/ear).

RESULTS

Rutin (27.81 ± 1.11 mg/g) was identified in CdE by HPLC analysis. The required amounts of CdE, rutin and ascorbic acid to reduce the initial concentration of radical DPPH by 50% (IC₅₀) were 7.77 (6.31-9.57) μg/mL, 3.62 (3.26-4.01) μg/mL and 3.74 (3.37-4.14) μg/mL with a radical DPPH reduction of 91 ± 1.2%, 91 ± 0.5%, and 96 ± 0.44% (at 30 μg/mL), respectively. Moreover, CdE and rutin presented H₂O₂ scavenging activity with H₂O₂ levels reduction of 41 ± 7% and 46 ± 6%, respectively and SOD-like activity of 60 ± 4% and 51 ± 14%, respectively. On the other hand, just rutin presented nitric oxide scavenging activity of 54 ± 6%. CdE and rutin topically applied inhibited the ear edema with a maximum inhibition of 70 ± 5% (1 mg/ear) and 78 ± 10% (0.03 mg/ear), respectively. Treatments reduced the MPO activity (42 ± 4% to CdE; 1mg/ear and 30 ± 8% to rutin; 0.03 mg/ear). Histologically, the topical treatments also reduced the dermis thickness and the inflammatory cells infiltration.

CONCLUSION

We demonstrated the antioxidant and anti-inflammatory effect of C.decandra leaves and rutin. Its antioxidant potential may contribute to inflammatory process attenuation, supporting the C.decandra leaves used as a promising alternative in the therapy of the inflammatory diseases.

[Topical Treatment of Pruritic Skin Disease and the Role of Community Pharmacists]

Itching, or pruritus, can be defined as an unpleasant sensation that evokes the desire to scratch. Pruritus is most commonly associated with a primary skin disorder such as atopic dermatitis (AD), psoriasis, etc., and can have a major impact on the quality of life of those patients. Itch-induced scratching can further damage the skin barrier, leading to a worsening of symptoms. For that reason, it is important to manage pruritus. Topical glucocorticoids are commonly the first-line therapy in the management of AD and psoriasis patients. We found that topical glucocorticoids induce pruritus in mice under certain conditions. Topical glucocorticoids may induce pruritus in a mouse model of allergic contact dermatitis via inhibition of prostaglandin (PG)D₂ production in antigen-mediated activated mast cells in the skin. Additionally, topical glucocorticoids do not induce pruritus in healthy skin. These results indicate the importance of controlling skin inflammation to a healthy level by applying sufficient quantities of glucocorticoids to avoid glucocorticoid-induced pruritus. However, topical "steroid phobia" is common in Japan, and most patients apply inadequate amounts of topical glucocorticoids for this reason. This may cause glucocorticoid-induced pruritus in patients by prolonging the skin inflammation. We conducted a survey regarding community pharmacists' instructions on the application quantity of topical glucocorticoids and found that most community pharmacists have experienced inappropriate instructions concerning this point.

Effects of 2'-3'-dihydroxy-4',6'-dimethoxychalcone derived from green perilla on auricle thickness in chronic contact dermatitis model mice

Oxidative stress has been implicated in the pathogenesis of allergic contact dermatitis. The nuclear factor erythroid 2-related factor 2 (Nrf2)-antioxidant response element (ARE) pathway, an in vivo antioxidant system, induces antioxidant enzymes. In our previous studies, we isolated 2',3'-dihydroxy-4',6'-dimethoxychalcone (DDC) from green perilla and identified it as a novel activator of the Nrf2-ARE pathway. We also discovered that it exerted cytoprotective effects against oxidative stress in PC12 cells. However, its effects on skin disease model animals in vivo remain unclear. In the present study, auricular thickness time-dependently increased with the repeated application of picryl chloride, and significant increases were observed from Day 2 in chronic contact hypersensitivity (cCHS) model mice. Histological changes, such as higher numbers of cells in the epidermis, were observed with increases in auricular thickness. The administration of DDC every two days from Day 6 suppressed the increases in auricular thickness and the number of scratching events in a dose-dependent manner. The expression levels of antioxidant enzymes increased in the mouse auricle 24 h after the administration of DDC. These results presume that DDC inhibits increases in auricular thickness in cCHS mice by up-regulating the expression of antioxidative enzymes through the activation of the Nrf2-ARE pathway.

Tissue-specific contributions of Tmem79 to atopic dermatitis and mast cell-mediated histaminergic itch

Atopic dermatitis (AD) is the most common skin disease in children. It is characterized by relapsing inflammation, skin-barrier defects, and intractable itch. However, the pathophysiology of itch in AD remains enigmatic. Here, we examine the contribution of Tmem79, an orphan transmembrane protein linked to AD in both mice and humans. We show that Tmem79 is expressed by both keratinocytes and sensory neurons, but that loss of keratinocytic Tmem79 is sufficient to elicit robust scratching. Tmem79-/- mice demonstrate an accumulation of dermal mast cells, which are diminished following chronic treatment with cyclooxygenase inhibitors and an EP3 receptor antagonist. In Tmem79-/- mice, mast cell degranulation produces histaminergic itch in a histamine receptor 1/histamine receptor 4 (H4R/H1R)-dependent manner that may involve activation of TRPV1- afferents. TMEM79 has limited sequence homology to a family of microsomal glutathione transferases and confers protection from cellular accumulation of damaging reactive species, and may thus play a role in regulating oxidative stress. In any case, mechanistic insights from this model suggest that therapeutics targeting PGE2 and/or H1R/H4R histaminergic signaling pathways may represent useful avenues to treat Tmem79-associated AD itch. Our findings suggest that individuals with mutations in Tmem79 develop AD due to the loss of protection from oxidative stress.

Attenuated Activation of Homeostatic Glucocorticoid in Keratinocytes Induces Alloknesis via Aberrant Artemin Production

Intense chronic itch significantly reduces quality of life for atopic dermatitis patients, impairing daily activity. Although abnormal itch sensation can be induced by innocuous stimuli, known as alloknesis, the mechanisms driving this process remain obscure. Psychological and environmental stimuli are known to aggravate atopic dermatitis symptoms. Recently, the enzyme 11β-hydroxysteroid dehydrogenase-1 (HSD11β1), which is expressed in keratinocytes, has been implicated in maintaining homeostasis against environmental stimuli by activating endogenous glucocorticoids. To investigate the role of HSD11β1 in keratinocytes, we generated keratinocyte-specific Hsd11b1-knockout (Hsd11b1^KC-/-) mice and analyzed skin phenotype. Hsd11b1^KC-/- mice exhibited abnormal cutaneous innervation and skin sensitivity, including light mechanical stimulus-evoked itch (i.e., alloknesis). Attenuated endogenous glucocorticoid activation induced by aberrant artemin production in keratinocytes was involved in alloknesis in Hsd11b1^KC-/- mice. Finally, we observed a significant negative correlation between expression of HSD11β1 and artemin in human skin with and without AD. These results suggest that endogenous glucocorticoids that maintain skin homeostasis in the epidermis affect both skin innervation and cutaneous sensation. Modulation of HSD11β1 activation could be a therapeutic target for sensitive or itchy skin.

Coriander alleviates 2,4-dinitrochlorobenzene-induced contact dermatitis-like skin lesions in mice

Contact dermatitis (CD) is a pattern of inflammatory responses in the skin that occurs through contact with external factors. The clinical picture is a polymorphic pattern of skin inflammation characterized by a wide range of clinical features, including itching, redness, scaling, and erythema. Coriandrum sativum L. (CS), commonly known as coriander, is a member of the Apiaceae family and is cultivated throughout the world for its nutritional and culinary values. Linoleic acid and linolenic acid in CS have various pharmacological activities. However, no study of the inhibitory effects of CS on CD has been reported. In this study, we demonstrated the protective effect of CS against 2,4-dinitrochlorobenzene-induced CD-like skin lesions. CS, at doses of 0.5-1%, applied to the dorsal skin inhibited the development of CD-like skin lesions. Moreover, the Th2-mediated inflammatory cytokines, immunoglobulin E, tumor necrosis factor-α, interferon-γ, interleukin (IL)-1, IL-4, and IL-13, were significantly reduced. In addition, CS increased the levels of total glutathione and heme oxygenase-1 protein. Thus, CS can inhibit the development of CD-like skin lesions in mice by regulating immune mediators and may be an effective alternative therapy for contact diseases.