Anti-allergic function and regulatory mechanisms of KR62980 in allergen-induced airway inflammation

Roles of PPAR activation in cancer therapeutic resistance: Implications for combination therapy and drug development

Therapeutic resistance is a major obstacle to successful treatment or effective containment of cancer. Peroxisome proliferator-activated receptors (PPARs) play an essential role in regulating energy homeostasis and determining cell fate. Despite of the pleiotropic roles of PPARs in cancer, numerous studies have suggested their intricate relationship with therapeutic resistance in cancer. In this review, we provided an overview of the roles of excessively activated PPARs in promoting resistance to modern anti-cancer treatments, including chemotherapy, radiotherapy, targeted therapy, and immunotherapy. The mechanisms through which activated PPARs contribute to therapeutic resistance in most cases include metabolic reprogramming, anti-oxidant defense, anti-apoptosis signaling, proliferation-promoting pathways, and induction of an immunosuppressive tumor microenvironment. In addition, we discussed the mechanisms through which activated PPARs lead to multidrug resistance in cancer, including drug efflux, epithelial-to-mesenchymal transition, and acquisition and maintenance of the cancer stem cell phenotype. Preliminary studies investigating the effect of combination therapies with PPAR antagonists have suggested the potential of these antagonists in reversing resistance and facilitating sustained cancer management. These findings will provide a valuable reference for further research on and clinical translation of PPAR-targeting treatment strategies.

Regulation of Immune Cell Function by PPARs and the Connection with Metabolic and Neurodegenerative Diseases

Increasing evidence points towards the existence of a bidirectional interconnection between metabolic disease and neurodegenerative disorders, in which inflammation is linking both together. Activation of members of the peroxisome proliferator-activated receptor (PPAR) family has been shown to have beneficial effects in these interlinked pathologies, and these improvements are often attributed to anti-inflammatory effects of PPAR activation. In this review, we summarize the role of PPARs in immune cell function, with a focus on macrophages and T cells, and how this was shown to contribute to obesity-associated inflammation and insulin resistance, atherosclerosis, and neurodegenerative disorders. We address gender differences as a potential explanation in observed contradictory results, and we highlight PPAR-induced metabolic changes as a potential mechanism of regulation of immune cell function through these nuclear receptors. Together, immune cell-specific activation of PPARs present a promising therapeutic approach to treat both metabolic and neurodegenerative diseases.

PPAR-γ promotes type 2 immune responses in allergy and nematode infection

A hallmark of immunity to worm infections and many allergies is a strong type 2 immune response. This is characterized by the production of cytokines interleukin-5 (IL-5) and IL-13 by adaptive T helper 2 (T_H2) cells and/or type 2 innate lymphoid cells. Peroxisome proliferator activated receptor-γ (PPAR-γ) is typically regarded as an anti-inflammatory factor. We report that T_H2 cells express high levels of PPAR-γ in response to the allergen house dust mite and after infection with the parasite Heligmosomoides polygyrus Mice lacking PPAR-γ in T cells failed to effectively differentiate into IL-5- and IL-13-secreting cells and, hence, did not develop T_H2 cell-associated pathologies, including goblet cell metaplasia and eosinophilia, in response to allergen challenge. Furthermore, these mice could not mount protective immune responses to nematode infection. In addition, mice lacking PPAR-γ in T cells had greatly reduced frequencies of T_H2 cells in visceral adipose tissue. Mechanistically, PPAR-γ appeared to promote the expression of the IL-33 receptor on the surface of T_H2 cells. These results pinpoint PPAR-γ as a factor that drives type 2 responses in allergy, worm infection, and visceral adipose tissue.

Suppression of Inflammatory cytokine production by ar-Turmerone isolated from Curcuma phaeocaulis

Rhizomes of Curcuma phaeocaulis Valeton (Zingiberaceae) have traditionally been used for controlling inflammatory conditions. Numerous studies have aimed to isolate and characterize the bioactive constituents of C. phaeocaulis. It has been reported that its anti-inflammatory properties are a result of cyclooxygenase-2 inhibition; however, its effect on the T-cell function remains to be elucidated. In this study, four known sesquiterpenoids, viz., ar-turmerone (TM), germacrone (GM), (+)-(4S,5S)-germacrone-4,5-epoxide (GE), and curzerenone (CZ), were isolated from C. phaeocaulis rhizomes and evaluated for their effects on the CD4(+) T-cell function. While GM, GE, and CZ had no effect on the activation of splenic T cells or CD4(+) T cells, TM suppressed the interferon (IFN)-γ production, without affecting the interleukin (IL)-4 expression. TM also decreased the expression of IL-2 in CD4(+) T cells, but did not change their cell-division rates upon stimulation. These results suggest that TM, a major constituent of C. phaeocaulis rhizomes selectively exerts potent anti-inflammatory effects via suppression of the inflammatory cytokines IFN-γ and IL-2.

Antiallergic Function of KR62980, a Peroxisome Proliferator-Activated Receptor-γ Agonist, in a Mouse Allergic Rhinitis Model

PURPOSE

Peroxisome proliferator-activated receptor γ (PPAR-γ) has been shown to play an important role in the control of inflammatory responses acting on macrophages, mast cells, T cells and eosinophils. A novel PPAR-γ ligand, KR62980 have been recently focused on due to the lower undesirable effects than other PPAR-γ ligands such as rosiglitazone and pioglitazone. The present study was aimed to investigate the effects of KR62980 on nasal symptoms and immunopathological profiles in allergic nasal mucosa in murine allergic rhinitis model.

METHODS

BALB/c mice were sensitized and challenged intranasally with ovalbumin (OVA). KR62980 was administered intraperitoneally or orally 3 hours before each intranasal OVA challenge.

RESULTS

Administration of KR62980 significantly decreased the number of nasal rubbing, nasal sneezing, ova-specific IgE and total IgE in serum, secretion of Interleukin (IL)-4, IL-5, and IL-17 from the spleen and eosinophilic infiltration in the nasal mucosa. KR62980 decreased the expression of IL-4, IL-5 and IL-10 mRNAs in the nasal mucosal tissue, while, it elevated the level of IL-10 and IFN-γ in splenocyte culture. KR62980 seemed to decrease IL-17 level in local and systemic level even though it did not reach to statistical significance. The anti-inflammatory effect was more definite when the KR62980 was administered intraorally than intraperitoneally.

CONCLUSIONS

A novel PPAR-γ ligand, KR62980 can attenuate OVA-induced allergic inflammation in mice mainly through modulation of Th2 cytokines. This finding suggests that PPAR-γ might have a role in the treatment of allergic rhinitis.

PPARγ Agonists in Adaptive Immunity: What Do Immune Disorders and Their Models Have to Tell Us?

Adaptive immunity has evolved as a very powerful and highly specialized tool of host defense. Its classical protagonists are lymphocytes of the T- and B-cell lineage. Cytokines and chemokines play a key role as effector mechanisms of the adaptive immunity. Some autoimmune and inflammatory diseases are caused by disturbance of the adaptive immune system. Recent advances in understanding the pathogenesis of autoimmune diseases have led to research on new molecular and therapeutic targets. PPARγ are members of the nuclear receptor superfamily and are transcription factors involved in lipid metabolism as well as innate and adaptive immunity. PPARγ is activated by synthetic and endogenous ligands. Previous studies have shown that PPAR agonists regulate T-cell survival, activation and T helper cell differentiation into effector subsets: Th1, Th2, Th17, and Tregs. PPARγ has also been associated with B cells. The present review addresses these issues by placing PPARγ agonists in the context of adaptive immune responses and the relation of the activation of these receptors with the expression of cytokines involved in adaptive immunity.

Nuclear receptors and their selective pharmacologic modulators

Nuclear receptors are ligand-activated transcription factors and include the receptors for steroid hormones, lipophilic vitamins, sterols, and bile acids. These receptors serve as targets for development of myriad drugs that target a range of disorders. Classically defined ligands that bind to the ligand-binding domain of nuclear receptors, whether they are endogenous or synthetic, either activate receptor activity (agonists) or block activation (antagonists) and due to the ability to alter activity of the receptors are often termed receptor "modulators." The complex pharmacology of nuclear receptors has provided a class of ligands distinct from these simple modulators where ligands display agonist/partial agonist/antagonist function in a tissue or gene selective manner. This class of ligands is defined as selective modulators. Here, we review the development and pharmacology of a range of selective nuclear receptor modulators.

Dose-independent pharmacokinetics of a new peroxisome proliferator-activated receptor-γ agonist, KR-62980, in Sprague-Dawley rats and ICR mice

The pharmacokinetics of a novel peroxisome proliferator-activated receptor-γ agonist, KR-62980, were characterized in vitro with respect to liver metabolic stability, cell permeability, and plasma protein binding and in vivo using Sprague-Dawley rats and ICR mice. The metabolic half-life of 0.1-10 μM KR-62980 was 11.5-15.2 min in rat liver microsomes and 25.8-28.8 min in human liver microsomes. KR-62980 showed high permeability across MDCK cell monolayers, with apparent permeability coefficients of 20.4 × 10(-6) to 30.8 × 10(-6) cm/sec. The plasma protein binding rate of KR-62980 was 89.4%, and most was bound to serum albumin. After intravenous administration of KR-62980 (2 mg/kg), the systemic clearance was 2.50 L/h/kg, and the volume of distribution at steady-state was 9.16 L/kg. The bioavailability after oral administration was approximately 60.9%. The dose-normalized AUC values were 0.50 ± 0.09, 0.41 ± 0.20, and 0.62 ± 0.08 h · μg/mL after oral administration of 2, 5, and 10 mg/kg KR-62980, respectively, showing no dose-dependency. The in vivo pharmacokinetic parameters in ICR mice were also dose independent. These data suggest that KR-62980 is not significantly dose dependent in rats or mice, although it may disappear rapidly from the systemic circulation via metabolism in the liver.

Treatment of allergic asthma: modulation of Th2 cells and their responses

Atopic asthma is a chronic inflammatory pulmonary disease characterised by recurrent episodes of wheezy, laboured breathing with an underlying Th2 cell-mediated inflammatory response in the airways. It is currently treated and, more or less, controlled depending on severity, with bronchodilators e.g. long-acting beta agonists and long-acting muscarinic antagonists or anti-inflammatory drugs such as corticosteroids (inhaled or oral), leukotriene modifiers, theophyline and anti-IgE therapy. Unfortunately, none of these treatments are curative and some asthmatic patients do not respond to intense anti-inflammatory therapies. Additionally, the use of long-term oral steroids has many undesired side effects. For this reason, novel and more effective drugs are needed. In this review, we focus on the CD4+ Th2 cells and their products as targets for the development of new drugs to add to the current armamentarium as adjuncts or as potential stand-alone treatments for allergic asthma. We argue that in early disease, the reduction or elimination of allergen-specific Th2 cells will reduce the consequences of repeated allergic inflammatory responses such as lung remodelling without causing generalised immunosuppression.

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.

Transcriptional regulation of T helper 17 cell differentiation

The third lineage of T helper subsets, Th17, has recently been identified as an IL- 17-producing CD4+ Th cell, and its functions and regulatory mechanisms have been extensively characterized in immune responses. Functional studies have provided evidence that Th17 cells are important for the modulation of autoimmune responses, such as chronic asthma, rheumatoid arthritis, inflammatory bowel diseases, and multiple sclerosis. Murine Th17 cell differentiation is enhanced by the coordinated functions of distinct cytokines including TGFbeta, IL-6, IL-21, and IL-23, whereas IL-2, IL-4, IFNgamma, and IL-27 inhibit its differentiation. In addition, Th17 cells are controlled by several transcription factors such as RORgammat, IRF4, BATF, FoxP3, T-bet, PPARgamma, E-FABP, and SOCSs. This review focuses on the functions and regulatory mechanisms of several transcription factors in the control of Th17 cell differentiation.