Up-regulation of peroxisome proliferator-activated receptor gamma in perennial allergic rhinitis

Imbalanced serum levels of resolvin E1 (RvE1) and leukotriene B4 (LTB4) in patients with allergic rhinitis

Timely and successful resolution of acute inflammation plays a crucial role in preventing the development of chronic airway inflammation in allergic rhinitis (AR). This study intends to assess the serum levels of pro-inflammatory leukotriene B4 (LTB4), anti-inflammatory mediators, including resolvin E1 (RvE1), RvD1, IL-10, and TGF-β, besides mRNA expression level of G-protein coupled receptor 120 (GPR120) and peroxisome proliferator-activated receptor-γ (PPAR-γ) receptors in peripheral blood leukocytes of AR patients. Thirty-seven AR patients and thirty age- and gender-matched healthy subjects were enrolled in this study. The serum levels of LTB4, RvE1, RvD1, IL-10, and TGF-β were measured using enzyme-linked immunosorbent assay (ELISA) technique, and the mRNA expression level of GPR120 and PPAR-γ was assessed by the real-time PCR method. The serum levels of RvE1 and LTB4 were significantly higher in patients with AR than in healthy subjects (P < 0.01 and P < 0.0001, respectively). However, a significantly lower ratio of RvE1 and RvD1 to LTB4 was found in patients with AR relative to healthy subjects (P < 0.05 and P < 0.0001, respectively). Likewise, the serum levels of both IL-10 and TGF-β cytokines were significantly reduced in patients with AR compared to healthy subjects (P < 0.01 and P < 0.0001, respectively). Furthermore, the mRNA expression of PPAR-γ was significantly lower in patients with AR than in healthy subjects (P < 0.05). Our findings indicate that imbalanced pro-resolving lipid mediator RvE1 and pro-inflammatory LTB4 might contribute to the defective airway inflammation-resolution and subsequent progression toward chronic inflammation in AR patients.

Pioglitazone attenuates allergic inflammation and induces production of regulatory T lymphocytes

BACKGROUND

Peroxisome proliferator-activated receptor gamma (PPAR-gamma) agonists have been shown to be involved in the regulation of allergic inflammatory responses. The molecular mechanisms by which PPAR-gamma activation inhibits the inflammatory process have not been well understood.

METHODS

BALB/c mice received ovalbumin (OVA) sensitization followed by OVA intranasal challenge. Mice in the treatment group received intragastric administration with pioglitazone (PIO; 30 mg/kg) before each OVA challenge. Various allergic responses were then assessed.

RESULTS

The frequencies of sneezing and nose-scratching and eosinophil infiltration decreased significantly in the PIO treatment group compared with the OVA group (p < 0.05). The PIO treatment also showed that the levels of nasal cavity lavage fluid interleukin (IL)-5 and sera OVA-specific immunoglobulin E (IgE) were markedly reduced (p < 0.05). PIO significantly increased the expression of Foxp3 mRNA (p < 0.05) and induced production of regulatory T lymphocyte (p < 0.01) compared with the OVA group.

CONCLUSION

Given the potent effectiveness shown by PIO, we conclude that PPAR-gamma agonists deserve investigation as potential therapies for human allergic upper airway inflammation.

Peroxisome Proliferator-Activated Receptor–γ Agonist Induces Regulatory T Cells in a Murine Model of Allergic Rhinitis

Objective. To evaluate the effects of peroxisome proliferator-activated receptor (PPAR)–γ agonist on the induction of regulatory T cells (Tregs) in a murine model of allergic rhinitis.

Study Design. Randomized controlled trial.

Setting. Animal study.

Subjects and Methods. BALB/c mice that received ovalbumin sensitization and challenge served as the ovalbumin group (n = 6). Two separate groups of 6 mice received intragastric administration with PPAR-γ agonist pioglitazone (30 mg/kg/d) or pioglitazone plus PPAR-γ antagonist GW9662 (0.5 mg/d) before each ovalbumin challenge. The control group (n = 6) was treated with drug vehicle alone. Various allergic responses were assessed. Real-time polymerase chain reaction was performed to investigate the mRNA expression of forkhead box P3 (Foxp3), T-bet, and GATA-3. Flow cytometry was used to determine the percentage of Tregs.

Results. Mice developed typical pathophysiological allergic rhinitis features after the ovalbumin challenge. The frequencies of sneezing and scratching were significantly decreased by pioglitazone treatment ( P < .0001). Eosinophils infiltration and the levels of interleukin-5 and interferon-γ in nasal cavity lavage fluid and sera immunoglobulin E were also markedly decreased by pioglitazone ( P < .001). The expression of Foxp3 mRNA and the population of Tregs were significantly increased by pioglitazone ( P < .05). Cotreatment with GW9662 reversed the anti-inflammatory effects of pioglitazone. The effects of PPAR-γ agonist on Foxp3 mRNA expression and Tregs induction were abrogated by administration of GW9662.

Conclusion. PPAR-γ agonist attenuates upper airway allergic inflammation in a PPAR-γ-dependent fashion, and the beneficial effects of pioglitazone in airway allergic inflammation may be mediated by induction of Tregs.

PPARgamma agonists upregulate the barrier function of tight junctions via a PKC pathway in human nasal epithelial cells

Peroxisome proliferator activated (PPAR)gamma plays a critical role in the control of not only adipocyte differentiation, lipid metabolism and immunity but also the barrier functions of epithelial and endothelial cells. In the present study, to investigate effects of PPAR gamma agonists on the tight junctional barrier of human nasal epithelial cells (HNECs), hTERT-transfected HNECs, which highly express both PPAR gamma and tight junction proteins, were treated with the PPAR gamma agonists rosiglitazone and troglitazone. Treatment with the PPAR gamma agonists enhanced the barrier function of hTERT-transfected HNECs together with the upregulation of tight junction molecules claudin-1 and -4, occludin, and tricellulin at the transcriptional level. A significant increase of tight junction strands was also observed after treatment with rosiglitazone. Treatment with PPAR gamma agonists induced the activity of phospho-PKC in hTERT-transfected HNECs. The upregulation of the tight junction molecules in hTERT-transfected HNECs by rosiglitazone was inhibited by not only PPAR gamma antagonists GW9662 and T0070907, but also the panPKC inhibitor GF109203X. These findings suggest that PPAR gamma agonists upregulate the barrier function of tight junctions of human nasal epithelial cells via a PKC signaling pathway and could be novel drugs for protection against inhaled substances and pathogens in the airway epithelium of human nasal mucosa.

Effect of peroxisome proliferator-activated receptor gamma agonists on myofibroblast differentiation and collagen production in nasal polyp-derived fibroblasts

OBJECTIVES

We investigated the effect of transforming growth factor-beta1 (TGF-beta1) on the differentiation of nasal polyp-derived fibroblasts (NPDFs) and on their production of collagen, and investigated the effect of peroxisome proliferator-activated receptor gamma (PPARgamma) agonists on the effects of TGF-beta1.

METHODS

Primary fibroblast lines were established from 5 human nasal polyp tissues. We activated the NPDFs with TGF-beta1 and exposed them to the PPARy agonists ciglitazone and 15-deoxy-Delta-prostaglandin J2. The expression of alpha-smooth muscle actin (alpha-SMA) and collagen was measured by reverse transcriptase-polymerase chain reactions, immunocytochemical staining, and collagen assays.

RESULTS

The treatment with TGF-beta1 increased the expression of alpha-SMA and collagen, and expression was markedly attenuated by the PPARy agonists.

CONCLUSIONS

PPARy agonists inhibit the differentiation of TGF-beta1-activated NPDFs and their production of collagen.

Peroxisome proliferator-activated receptor gamma negatively regulates allergic rhinitis in mice

BACKGROUND

Peroxisome proliferator-activated receptor gamma(PPAR-gamma) has been shown to play an important role in the control of inflammatory responses acting on macrophages, mast cells, T cells, and eosinophils. The present study was aimed at investigating the effects of PPAR-gamma agonist on nasal symptoms and eosinophil accumulations in nasal mucosa by using a murine allergic rhinitis model. Furthermore, we examined the expression of PPAR-gamma in the nasal mucosa in mice.

METHODS

BALB/c mice were sensitized and challenged intranasally with ovalbumin. Ciglitazone, a PPAR-gamma agonist, was administered orally 6 hours before each nasal challenge.

RESULTS

Administration of PPAR-gamma agonist significantly decreased the number of nasal rubs, nasal histamine responsiveness, serum IgE, IL-5 production from the spleen, and eosinophilic infiltration in the nasal mucosa. Furthermore, PPAR-gamma was expressed in eosinophils and epithelial cells in the nasal mucosa by immunohistochemistry.

CONCLUSIONS

PPAR-gamma was expressed in eosinophils and epithelial cells in the nasal mucosa. Also, the oral administration of ciglitazone is effective in upper airway allergic inflammation in mice.