Establishment of an in vitro test system to evaluate the down-regulatory activities of natural products on IL-4

Therapeutic strategies in extrinsic atopic dermatitis: focus on inhibition of IL-4 as a new pharmacological approach

INTRODUCTION

Recent data about atopic dermatitis (AD) pathogenesis postulate that T cells and their related cytokines and chemokines are primarily responsible for the inflammatory responses.

AREAS COVERED

AD, the primary complex disease associated with filaggrin deficiency, is characterized by cutaneous inflammation driven by type 2 helper T (TH2) cells. TH2-related molecules, such as IL-4, IL-13, dominate the immune infiltrate. Experimental evidences suggest that these cytokines may be considered attractive therapeutic targets in AD, particularly in extrinsic AD with IgE overproduction. Recently, a fully human monoclonal antibody directed against the IL-4 receptor α subunit blocking IL-4 and IL-13 signaling has been evaluated in Phase I and Phase II clinical trials in patients with moderate-to-severe AD with significant improvement in disease severity. Phase III trials are ongoing.

EXPERT OPINION

Treatment of AD represents a therapeutic challenge. TH2 cytokine-targeted therapies represent promising treatment options that could improve the therapeutic armamentarium for AD. These therapies are likely to become future therapeutic options in AD, particularly in the extrinsic AD.

Cyanidin-3-glucoside suppresses Th2 cytokines and GATA-3 transcription factor in EL-4 T cells

Allergic disease is dominated by Th2 immune responses. Interleukin (IL)-4 and IL-13, representative Th2 cytokines, play pivotal roles in the pathogenic activation of the Th2 immune response. In this study, we found that cyanidin-3-glucoside chloride (C3G), an anthocyanin suppressed IL-4 and IL-13 produced in activated EL-4 T cells but not Th1 cytokines including IL-2, interferon-γ, or IL-12. IL-4 and IL-13 mRNA levels and luciferase activation in cells transiently transfected with IL-4 and IL-13 promoter reporter plasmids were significantly inhibited by C3G, suggesting that suppression might be, at least in part, regulated at the transcriptional level. Data from western blot and reverse transcription-polymerase chain reaction analyses of transcription factors involved in cytokine expression suggested that expression of GATA-3, but not T-bet, was downregulated in the nucleus by C3G. Taken together, our data indicate that C3G may has potential as an anti-allergic agent suppressing Th2 activation by downregulating Th2 cytokines and the GATA3 transcription factor in allergies.

Eicosapentaenoic acid and docosahexaenoic acid suppress Th2 cytokine expression in RBL-2H3 basophilic leukemia cells

It is known that the intake of omega-3 fatty acids, such as eicosapentaenoic (EPA) and docosahexaenoic acid (DHA), is beneficial for preventing and/or treating allergic diseases. The pathogenesis of allergic diseases is associated with overactivation of Th2-skewed immunity. Basophils generate large amounts of Th2 cytokines such as interleukin (IL)-4 and IL-13, which are critically involved in allergic inflammation. We investigated how EPA and DHA affect Th2 cytokine expression in phorbol 12-myristate 13-acetate- and ionomycin (PI)-activated RBL-2H3 basophilic leukemia cells. EPA and DHA induced a dramatic decrease in the production of IL-4 and IL-13 and their transcription in a dose-dependent manner. Luciferase assays of RBL-2H3 cells stably expressing Il4 and Il13 promoter-reporter plasmids demonstrated a significant suppression of PI-induced promoter activation. Analysis of certain transcription factors revealed that nuclear expression of c-Fos and the mRNA expression were suppressed by EPA and DHA. Furthermore, they significantly inhibited the nuclear expression and translocation of nuclear factor of activated T cells (NF-AT)1. In contrast, the expression levels of nuclear factor kappa-B (NF-κB), GATA-binding proteins (GATAs), and CCAAT/enhancer binding protein alpha (C/EBPα) were not significantly affected by EPA and DHA. Phosphorylation of extracellular signal-related kinase was inhibited by EPA and DHA, and phosphorylation of p38 mitogen-activated protein kinase was decreased by DHA, but not by EPA. Taken together, our data suggest that EPA and DHA may suppress Th2-skewed allergic immune responses by inhibiting the expression of basophilic IL-4 and IL-13.

Suppressive effects of fructus of Magnolia denudata on IL-4 and IL-13 expression in T cells

Magnolia species have been used for the treatment of allergic diseases in Asia as folk medicine; however, the cellular and molecular mechanisms of its anti-allergic effects have rarely been investigated. In this study, we demonstrated that a methanolic extract of the fructus of Magnolia denudata has suppressive effects on Th2 cytokine production such as IL-4 and IL-13, but not IFN-γ and IL-17, produced by both phorbol 12-myristate 13-acetate/ionomycin (PI)- and CD3/CD28-stimulated EL-4 T cells. Moreover, the mRNA expression of Th2 cytokines was significantly inhibited, and luciferase activity in cells transiently transfected with IL-4 or IL-13 promoter reporter plasmids was suppressed by M. denudata, indicating that M. denudata may regulate these expression at the transcriptional level. Western blot analysis for transcription factors involved in the cytokine gene expression indicated that the activation of c-Jun was significantly downregulated in the nucleus of cells, while the activations of nuclear factor of activated T cells, nuclear factor kappa B and c-Fos, were not affected. Furthermore, the mRNA expression and nuclear translocation of GATA-binding protein 3, a key transcriptional factor for Th2 commitment and Th2 cytokine expression, but not T-bet and RORγt, were dramatically downregulated by M. denudata. Treatment with M. denudata suppressed the phosphorylation of p38 mitogen-activated protein kinase; however, the PI-induced phosphorylation of extracellular signal-related kinase and c-Jun N-terminal kinase was unaffected. Taken together, our study indicated that M. denudata inhibited IL-4 and IL-13 expression, possibly through regulation of p38 mitogen-activated protein kinase phosphorylation and selective transcription factors, such as GATA-3 and c-Jun, in EL-4 T cells.

G-quadruplex-binding benzo[a]phenoxazines down-regulate c-KIT expression in human gastric carcinoma cells

There is considerable interest in the structure and function of G-quadruplex nucleic acid secondary structures, their cellular functions, and their potential as therapeutic targets. G-Quadruplex sequence motifs are prevalent in gene promoter regions and it has been hypothesized that G-quadruplex structure formation is associated with the transcriptional status of the downstream gene. Using a functional cell-based assay, we have identified two novel G-quadruplex ligands that reduce the transcription of a luciferase reporter driven from the G-quadruplex-containing c-KIT promoter. We have further shown that endogenous c-KIT expression in a human gastric carcinoma cell line is also reduced on treatment with these molecules. Biophysical analysis using surface plasmon resonance has shown that these molecules preferentially bind with high affinity to one of the two G-quadruplex sequences in the c-KIT promoter over double-stranded DNA. This work highlights the utility of cell-based reporter assays to identify new G-quadruplex binding molecules that modulate transcription and identifies benzo[a]phenoxazine derivatives as potential antitumor agents.

Suppressive effects of T-412, a flavone on interleukin-4 production in T cells

Interleukin (IL)-4 has been suggested as a molecular therapeutic target to prevent and/or treat various allergic diseases and several flavonoids have been suggested as anti-allergic agents suppressing IL-4 production. In an effort to find novel candidates for anti-allergic agents from natural sources, we screened several flavonoids affecting on IL-4 production. In this study, we showed that 7,8,4'-trihydroxyflavone (T-412) significantly decreased IL-4 production both in phorbol 12-myristate 13-acetate (PMA) and ionomycin (PI)-activated EL-4 T cells and concanavalin A (ConA)-activated murine CD4(+) T cells in a dose- and time-dependent manner. The PI-induced increase of IL-4 mRNA expression was dramatically suppressed by T-412 at 6 h, indicating the suppression is regulated at transcriptional level. T-412 also significantly inhibited IL-4 gene promoter activity in EL-4 T cells transiently transfected with luciferase reporter plasmid containing IL-4 promoter (pGL4.14-IL-4). Western blot analysis of the transcription factors revealed that T-412 suppressed the nuclear expression of nuclear factor of activated T cells (NF-AT)c1, c-Jun and c-Maf, but not c-Fos and nuclear factor kappa B (NF-kappaB). Our data suggested that T-412 might have potential as a candidate for anti-allergic agent having suppressive effects on IL-4 production in activated T cells by controlling the transcription of IL-4.