Elsevier

International Immunopharmacology

Volume 73, August 2019, Pages 343-352
International Immunopharmacology

Betulinic acid suppresses Th17 response and ameliorates psoriasis-like murine skin inflammation

https://doi.org/10.1016/j.intimp.2019.05.030Get rights and content

Highlights

  • Betulinic acid alleviates psoriatic symptoms and the skin lesion in mice.

  • It reduces IL-17+CD4+ and IL-17+γδTCR+ T cell frequency in the psoriatic mice.

  • It also lowers proinflammatory cytokine levels in the skin lesion such as IL-17A.

  • Treatment with betulinic acid inhibits NFκB signaling in psoriatic mouse skin.

Abstract

Psoriasis is a common inflammatory skin disease. Current treatment for psoriasis relies on conventional immunosuppressive agents. However, long-term treatment with global immunosuppression may cause various side effects. Thus, it is compelling to seek alternative drugs for treating psoriasis with potentially less side effects. Betulinic acid (BA) is a naturally occurring pentacyclic triterpene, an ingredient that originally exists in natural plants and lacks systemic toxicity. BA can regulate immunity with anti-fibrotic, anti-inflammatory and antioxidant properties. However, it's unknown whether BA has a therapeutic effect on psoriasis. The objectives of this study were to investigate whether BA attenuates psoriatic skin inflammation and to identify its mechanisms of action. A murine model of imiquimod-induced psoriasis was utilized to evaluate skin lesion while flow cytometry, immunohistochemistry, quantitative RT-PCR and Western blotting analyses were performed for immunoassays. We found that BA treatment alleviated psoriatic symptoms and inflammatory skin lesion. BA lowered the PASI scores, decreased epidermal thickness and reduced T cell infiltration in the skin lesion. Moreover, BA reduced the frequency of IL-17A-expressing CD4+ and γδ T cells in psoriatic mice, but did not alter CD4+FoxP3+ Treg frequency. BA also reduced IL-17A production but increased anti-inflammatory cytokine IL-10 level in serum of the psoriatic mice. Furthermore, BA inhibited gene expression of pro-inflammatory mediators in skin lesions, including RORγt, IL-17A, IL-6 and TNFα. Importantly, it suppressed NFκB signaling in the skin lesion. Finally, BA inhibited T cell proliferation and IL-17A production by CD4+ T-Cells in vitro. Thus, BA attenuates psoriasis and inhibits Th17 development.

Introduction

Psoriasis is an immune-mediated, chronic and inflammatory skin disorder that affects approximately 2–3% of the general population worldwide, characterized by thickening and redness of the skin with pronounced keratinocyte hyperproliferation, dermal/epidermal hyperplasia and inflammatory cell infiltration [[1], [2], [3]]. Conventional immunosuppressive agents, including methotrexate (MTX) and cyclosporine, have been widely used to treat psoriasis [4,5]. However, various adverse reactions have limited their clinical application. Furthermore, the pathogenic mechanisms underlying psoriasis have not been fully understood. It is generally accepted that the immunopathology of psoriasis is mainly mediated and propagated by T cells [6,7]. In addition, a variety of proinflammatory cytokines have been implicated in the pathogenesis of psoriasis [[8], [9], [10]]. Thus, the pathogenesis of psoriasis is mainly caused by autoimmune-mediated skin inflammation.

Betulinic acid (BA), 3β-hydroxy-lup-20(29)-en-28-oic acid, is a naturally occurring pentacyclic triterpenoid [11], which was originally extracted from many species of plants [12,13], including the birch tree, birch bark oil (betulae pix) [[14], [15], [16]] and paeoniaceae [[17], [18], [19]]. BA has been reported to possess various biological properties, including anti-inflammatory [20,21], anti-cancer [22,23], anti-fibrotic [24], anti-angiogenic [25] and antioxidant activities [26]. In recent years, BA has been reported to inhibit the production of several pro-inflammatory mediators or cytokines [20,27]. Many studies have demonstrated that BA is also an immunomodulatory agent [[28], [29], [30], [31], [32], [33], [34]]. However, therapeutic effects of BA on psoriasis and its potential mechanisms of action remain unclear. In this study, we found that BA ameliorated imiquimod (IMQ)-induced psoriasis-like skin lesion in mice by downregulating Th17 and IL-17+ γδ T cell development. Furthermore, BA inhibited the gene expression of pro-inflammatory mediators in the skin lesion, including RORγt, IL-17A, IL-6 and TNFα. Importantly, it also suppressed NFκB signaling in the skin of the psoriatic mice. Finally, BA inhibited T cell proliferation and IL-17A production by CD4+ T-Cells in vitro. Thus, BA could be a natural anti-psoriatic drug for treating human psoriasis.

Section snippets

Animals

BALB/c and C57BL/6 male mice (18–20 g, 6–8 weeks old) were purchased from Guangdong Medical Laboratory Animal Center (Guangzhou, Guangdong, China). All mice were housed under specific pathogen-free condition, with free access to food and water. This study was carried out in accordance with the National Guidelines for the Care and Use of Laboratory Animals and approved by the Institutional Animal Care and Use Committee of Guangdong Provincial Academy of Chinese Medical Sciences.

IMQ-induced murine psoriatic skin disease

Dorsal hair of

BA ameliorates IMQ-induced psoriatic skin lesion in mice

To determine whether BA would have an effect on psoriasis, we utilized a model of IMQ-induced psoriatic mice that were treated with or without BA. The morphological observations and PASI scores are shown in Fig. 1A and Fig. 1D. Control mice without IMQ had normal skin without any sign of inflammation. However, psoriasis-like lesions, including skin erythema, scaling and thickening, were severe in model group on day 8 following IMQ treatment. Treatments with either low-doses of BA (BA-L:

Discussion

Psoriasis is a common, chronic and inflammatory skin disorder that affects patients physically and psychologically [38]. The precise etiology of psoriasis remains poorly understood although it may result from autoimmunity [39]. Currently, several approaches are available for the treatment of psoriasis, including immunosuppressive agents MTX and cyclosporine. However, due to long-term global immunosuppression, a conventional immunosuppressant may cause severe side effects, including organ

Author contributions

CL and YC: Formal analysis, investigation, methodology and writing-original draft; ChL: Funding acquisition and supervision; HC, JD, YY and YYX: Formal analysis; HL: Methodology; HH, JW and LH: Resources; and ZD: Conceptualization and writing-review & editing.

Declaration of Competing Interest

None.

Acknowledgments

This study was supported by National Natural Science Foundation of China (81803804); Natural Science Foundation of Guangdong Province (S2013030011515, 2017A030310124 and 2018A030310530); Specific Research Fund for TCM Science and Technology of Guangdong Provincial Hospital of Chinese Medicine (YN2016ZD01 and YN2015MS20); and Science and Technology Planning Project of Guangdong Province (2017A050506041 and 2017B030314166), China.

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