Yun Ho Choi

Inhibition of Protein Kinase C Delta Attenuates Allergic Airway Inflammation through Suppression of PI3K/Akt/mTOR/HIF-1 Alpha/VEGF Pathway

Vascular endothelial growth factor (VEGF) is supposed to contribute to the pathogenesis of allergic airway disease. VEGF expression is regulated by a variety of stimuli such as nitric oxide, growth factors, and hypoxia-inducible factor-1 alpha (HIF-1α). Recently, inhibition of the mammalian target of rapamycin (mTOR) has been shown to alleviate cardinal asthmatic features, including airway hyperresponsiveness, eosinophilic inflammation, and increased vascular permeability in asthma models. Based on these observations, we have investigated whether mTOR is associated with HIF-1α-mediated VEGF expression in allergic asthma. In studies with the mTOR inhibitor rapamycin, we have elucidated the stimulatory role of a mTOR-HIF-1α-VEGF axis in allergic response. Next, the mechanisms by which mTOR is activated to modulate this response have been evaluated. mTOR is known to be regulated by phosphoinositide 3-kinase (PI3K)/Akt or protein kinase C-delta (PKC δ) in various cell types. Consistent with these, our results have revealed that suppression of PKC δ by rottlerin leads to the inhibition of PI3K/Akt activity and the subsequent blockade of a mTOR-HIF-1α-VEGF module, thereby attenuating typical asthmatic attack in a murine model. Thus, the present data indicate that PKC δ is necessary for the modulation of the PI3K/Akt/mTOR signaling cascade, resulting in a tight regulation of HIF-1α activity and VEGF expression. In conclusion, PKC δ may represent a valuable target for innovative therapeutic treatment of allergic airway disease.

Silibinin attenuates allergic airway inflammation in mice

Allergic asthma is a chronic inflammatory disease regulated by coordination of T-helper2 (Th2) type cytokines and inflammatory signal molecules. Silibinin is one of the main flavonoids produced by milk thistle, which is reported to inhibit the inflammatory response by suppressing the nuclear factor-kappa B (NF-κB) pathway. Because NF-κB activation plays a pivotal role in the pathogenesis of allergic inflammation, we have investigated the effect of silibinin on a mouse ovalbumin (OVA)-induced asthma model. Airway hyperresponsiveness, cytokines levels, and eosinophilic infiltration were analyzed in bronchoalveolar lavage fluid and lung tissue. Pretreatment of silibinin significantly inhibited airway inflammatory cell recruitment and peribronchiolar inflammation and reduced the production of various cytokines in bronchoalveolar fluid. In addition, silibinin prevented the development of airway hyperresponsiveness and attenuated the OVA challenge-induced NF-κB activation. These findings indicate that silibinin protects against OVA-induced airway inflammation, at least in part via downregulation of NF-κB activity. Our data support the utility of silibinin as a potential medicine for the treatment of asthma.

Polydatin inhibits mast cell-mediated allergic inflammation by targeting PI3K/Akt, MAPK, NF-κB and Nrf2/HO-1 pathways

Polydatin(PD) shows anti-allergic inflammatory effect, and this study investigated its underlying mechanisms in in vitro and in vivo models. IgE-mediated passive cutaneous anaphylaxis (PCA) and passive systemic anaphylaxis (PSA) models were used to confirm PD effect in vivo. Various signaling pathway proteins in mast cell were examined. RT-PCR, ELISA and western blotting were applied when appropriate. Activity of Lyn and Fyn kinases in vitro was measured using the Kinase Enzyme System. PD dose-dependently reduced the pigmentation of Evans blue in the PCA model and decreased the concentration of serum histamine in PSA model, and attenuated the degranulation of mast cells without generating cytotoxicity. PD decreased pro-inflammatory cytokine expression (TNF-α, IL-4, IL-1β, and IL-8). PD directly inhibited activity of Lyn and Syk kinases and down-regulated downstream signaling pathway including MAPK, PI3K/AKT and NF-kB. In addition, PD also targets Nrf2/HO-1 pathway to inhibit mast cell-derived allergic inflammatory reactions. In conclusion, the study demonstrates that PD is a possible therapeutic candidate for allergic inflammatory diseases. It directly inhibited activity of Lyn and Syk kinases and down-regulates the signaling pathway of MAPK, PI3K/AKT and NF-κB, and up-regulates the signaling pathway of Nrf2/HO-1 to inhibit the degranulation of mast cells.

The role of mast cells in atrial natriuretic peptide-induced cutaneous inflammation

Atrial natriuretic peptide (ANP) is widely distributed throughout the heart, skin, gastrointestinal and genital tracts, and nervous and immune systems. ANP acts to mediate vasodilation and induces mast cell activation in both human and rats in vitro. However, the mechanisms of ANP-induced mast cell activation, the extent to which ANP can induce tissue swelling, mast cell degranulation, and granulocyte infiltration in mouse skin are not fully understood. This issue was investigated by treatment with ANP in rat peritoneal mast cells (RPMCs) and mouse peritoneal mast cells (MPMCs) in vitro and by injection of ANP into the skin of congenic normal WBB6F1/J-Kit+/Kit+ +/+, genetically mast cell-deficient WBB6F1/J-Kit(W)/Kit(W-v) (W/W(v)) and mast cell-engrafted W/W(v) (BMCMC→W/W(v)) mice in vivo. ANP induced the release of histamine and TNF-α from RPMCs and enhanced serotonin release from MPMCs, in a dose-dependent fashion, as well as reduced cAMP level of RPMCs in vitro. In +/+ mice, ANP induced significant tissue swelling, mast cell degranulation, and granulocyte infiltration in a dose-dependent manner, whereas not in genetically mast cell-deficient W/W(v) mice. However, ANP-induced cutaneous inflammation has been restored in BMCMC→W/W(v) mice. These data indicate that mast cells play a key role in the ANP-induced cutaneous inflammation.

Recombinant Pyrin Domain Protein Attenuates Allergic Inflammation by Suppressing NF-κB Pathway in Asthmatic Mice

Pyrin domain (PYD), a subclass of protein motif known as the death fold, is frequently involved in inflammation and immune responses. PYD modulates nuclear factor‐kappa B (NF‐κB) signalling pathway upon various stimuli. Herein, a novel recombinant pyrin domain protein (RPYD) was generated. Its role and mechanism in inflammatory response in an ovalbumin (OVA) induced asthma model was investigated. After OVA challenge, there was inflammatory cell infiltration in the lung, as well as airway hyper‐responsiveness (AHR) to inhaled methacholine. In addition, eosinophils increased in the bronchoalveolar lavage fluids, alone with the elevated levels of Th‐2 type cytokines [interleukin (IL)‐4, IL‐5 and IL‐13], eotaxin, and adhesion molecules. However, the transnasal administration of RPYD before the OVA challenge significantly inhibited these asthmatic reactions. Moreover, RPYD markedly suppressed NF‐κB translocation, reduced phosphorylation of p38 MAPK, and thus attenuated the expression of intercellular adhesion molecule 1 and IL‐6 in the BEAS‐2B cells stimulated by proinflammatory cytokines in vitro. These findings indicate that RPYD can protect asthma host from OVA‐induced airway inflammation and AHR via down‐regulation of NF‐κB and p38 MAPK activities. RPYD may be used as a potential medicine for the treatment of asthma in clinic.

Asiaticoside Mitigates the Allergic Inflammation by Abrogating the Degranulation of Mast Cells

The effects of asiaticoside (AS) on allergic responses mediated by mast cells were investigated. AS showed no obvious cytotoxicity on RPMCs (rat peritoneal mast cells). AS reduced the intracellular calcium in RPMCs and deprived the histamine release and degranulation. AS also decreased the generation of antigen-induced tumor necrosis factor α, interleukin (IL)-4, IL-8, and IL-1β in RBL-2H3 cells sensitized by IgE. The suppression of AS on pro-inflammatory cytokines was related with the activation of the intracellular FcεRI and the inhibition of the nuclear factor-κB signaling pathway. In addition, AS disabled the phosphorylation of antigen-induced Syk, Lyn, Gab2, and PLCγ1, thus suppressing the downstream Akt phosphorylation and MAPKs pathways. It also increased HO-1 and Nrf2 expression time dependently. In summary, we demonstrate that AS suppresses the allergic inflammation mediated by mast cells and this effect might be mediated by FcεRI-dependent signaling pathways.