BACKGROUND: Shegan-Mahuang Decoction (SMD) is a classical formula that has been used to effectively treat cold-induced asthma (CA) for 1800 years. Airway smooth muscle cells (ASMCs) play a crucial role in airway remodeling of CA and can be modulated through bitter taste-sensing type 2 receptors (TAS2Rs). Given that SMD contains numerous bitter herbs and TAS2R10 expression in ASMCs remains consistently high, it is pertinent to explore whether SMD regulates ASMCs via TAS2R10 to exert its CA mechanism.
OBJECTIVE: This study investigated the efficacy as well as the potential mechanism of SMD in CA.
METHODS: In this study, experiments in vivo were conducted using the CA rat model induced by ovalbumin (OVA) along with cold stimulation. The effects of SMD and TAS2R10 expression in CA rats were evaluated using the following methods: clinical symptoms, weights, pathological staining, immunofluorescence staining (IF), enzyme-linked immunosorbent assay (ELISA), real-time quantitative polymerase chain reaction (RT-qPCR) and Western blot (WB). Assays in vitro including cell counting Kit-8 (CCK-8), ELISA, flow cytometry, TUNEL staining, RT-qPCR and WB were performed to investigate potential mechanism of SMD on the proliferation and apoptosis of ASMCs through upregulation of TAS2R10.
RESULTS: The administration of SMD resulted in a notable improvement in the symptoms, trends in weight, airway inflammation and airway remodeling observed in CA rats with upregulated TAS2R10. Mechanistically, we furtherly confirmed that SMD inhibits p70S6K/CyclinD1 pathway by upregulating TAS2R10. SMD furthermore blocked the G0/G1 phase, suppressed the proliferation and inducted apoptosis in ASMCs induced by platelet-derived growth factor-BB (PDGF-BB). Erythromycin (EM), a TAS2R10 agonist, can intensify these effects.
CONCLUSIONS: SMD significantly ameliorates CA by upregulating TAS2R10 and inhibiting the p70S6K/CyclinD1 pathway, thereby modulating ASMCs\' proliferation and apoptosis. Inspired by the Five Flavors Theory of Traditional Chinese Medicine, this study provides an updated treatment perspective for treating CA.

BACKGROUND: Shegan-Mahuang Decoction (SMD), also named Yakammaoto or Shegan-Mahuang Tang, is a classic formula of traditional Chinese medicine with nine herbs, including Asarum sieboldii Miq., Aster tataricus L.f., Ephedra sinica Stapf, Belamcanda chinensis (L.) Redouté, Pinellia ternata (Thunb.) Breit., Schisandra chinensis (Turcz.) Baill., Tussilago farfara L., Zingiber officinale Roscoe, and Ziziphus jujuba Mill. SMD was originally discovered by Zhang Zhongjing in Eastern Han dynasty. It has been widely used as traditional medicine to treat flu-like symptoms in China and Japan for around twenty centuries. It was also utilized for the treatment of the early stage of acute asthma. However, the immune mechanisms underlying its therapeutic effects remain unknown.
OBJECTIVE: This study was set to investigate the effects of SMD on asthmatic airway hyperresponsiveness and its impacts on adaptive immunity in a mouse model of asthma.
METHODS: The HPLC fingerprint profile of the water extract of SMD recorded 22 peaks, including those equivalent to guanosine, chlorogenic acid, tectoridin, 6-gingerol and wuweizisu B, as described previously (Yen et al., 2014). Airway hyperresponsiveness was assessed by measuring the airway resistance. Cellular infiltration was measured via H&E staining and immunochemistry while gene expression was analyzed using real-time RT-PCR. Treg frequency was determined through flow analysis whereas cytokine production in the supernatant was evaluated using ELISA. Finally, mTOR and NF-kB signalings were analyzed via Western blotting.
RESULTS: We found that SMD largely corrected the imbalance of Th cell subsets in asthmatic mice with a significant inhibition of Th2 and Th17 cytokine production, thereby reducing asthmatic airway hyperresponsiveness. Moreover, lung function tests showed that SMD reduced airway hyperresponsiveness while immunohistochemical analyses demonstrated that SMD attenuated pulmonary infiltration of CD3+ and CD4+ T cells. Further, we observed a significant increase in the proportion of CD4+Foxp3+ Tregs in SMD-treated asthmatic mice. We also found that SMD downregulated gene expression of GATA3 and ROR-γt in murine lung tissue. In addition, both mTOR- and NF-kB-related protein expressions were reduced in the lung tissue of SMD-treated mice. SMD inhibited Th2/Th17 cytokine production by CD4+ T cells and also their mTOR activity in vitro.
CONCLUSIONS: Our findings demonstrate that SMD attenuates asthmatic airway hyperresponsiveness by hindering Th2/Th17 differentiation, promoting CD4+FoxP3+ Treg generation and suppressing mTOR and NF-kB activities.