Inhibitory effects of Schizandrae Fructus on eotaxin secretion in A549 human epithelial cells and eosinophil migration

Abstract

Eosinophilia have been implicated in a broad range of diseases, most notably allergic conditions (e.g. asthma, rhinitis and atopic dermatitis) and inflammatory diseases. These diseases are characterized by an accumulation of eosinophils in the affected tissue. Defining the mechanisms that control the recruitment of eosinophil is fundamental to understanding how these diseases progress and identifying a novel target for drug therapy. Accordingly, this study was conducted to evaluate the regulatory effect of Schizandrae Fructus (SF) on the expression of eotaxin, an eosinophil-specific chemokine released in respiratory epithelium following allergic stimulation, as well as its effects on eosinophil migration.

To accomplish this, human epithelial lung cells (A549 cell) were stimulated with a combination of TNF-α (100 ng/ml) and IL-4 (100 ng/ml) for 24 h. The cells were then restimulated with TNF-α (100 ng/ml) and IL-1β (10 ng/ml) to induce the expression of chemokines and adhesion molecules involved in eosinophil chemotaxis for another 24 h. Next, the samples were treated with various concentrations of Schizandrae Fructus (SF) (1, 10, 100, 1000 μg/ml) or one of the major constituents of SF, schizandrin (0.1, 1, 10, 100 μg/ml), after which following inhibition effect assay was performed triplicates in three independence.

The levels of eotaxin in secreted proteins were suppressed significantly by SF (100 and 1000 μg/ml, p<0.01) and schizandrin (10 and 100 μg/ml, p<0.01). In addition, SF (1, 10, 100 and 1000 μg/ml) decreased mRNA expression levels in A549 cells significantly (p<0.01). Eosinophil recruitment to lung epithelial cells was also reduced by SF, which indicates that eotaxin plays a role in eosinophil recruitment. Furthermore, treatment with SF suppressed the expression of another chemokine, IL-8 (0.1 and 1 μg/ml SF, p<0.01), as well as intercellular adhesion molecule-1 (10 and 100 μg/ml SF, p<0.01) and vascular cell adhesion molecule-1 (0.1 and 1 μg/ml SF, p<0.05), which are all related to eosinophil migration. Taken together, these findings indicate that SF may be a desirable medicinal plant for the treatment of allergic diseases.

Introduction

Because exposure to environmental hazards is inevitable, outbreaks of allergic diseases such as allergic asthma, atopic dermatitis, and allergic rhinitis have increased. Indeed, in the United States more than 50 million people suffer from allergic diseases each year, costing the US health care system approximately $18 billion annually (Elsner et al. 2004). As a result, many academic and industrial studies have been conducted to define disease mechanisms and develop therapies to treat or prevent the symptoms of allergies.

The initial stage of asthmatic symptoms is airway inflammation, in which eosinophils play a crucial role (Kay 1991). Eosinophils are present in excess in the airways of asthma patients; however, their accumulation decreases with subsidence of the symptoms of asthma. During an asthma attack, eosinophils selectively migrate and adhere to vascular endothelial cells, after which they migrate into the airways in response to chemokine recruitment. Once in the airway, they infiltrate and cause inflammation (Djukanovic et al. 1992).

Many natural products used in traditional oriental medicine are reportedly good agents for the treatment of asthma (Lima-Landman et al. 2007). For example, it has been suggested that Moutan Cortex Radicis reduced eotaxin secretion (Kim et al. 2007). However, despite their remarkable ability to treat asthma, most natural products have not been widely used in western societies, because little is known about the modes of action at the molecular level. One such product, Schizandrae Fructus (SF) is the fruit of Schizandra chinensis Baill. SF, which is an oriental herb that contains schizandrin as one of its major constituents, is used by traditional oriental clinicians to treat several diseases including hepatitis (Liu 1989; Liu and Lesca 1982), and cancer (Li 1991). Accordingly, there have been several studies conducted to evaluate the molecular mechanisms responsible for the anti-tumor effects (Huang et al. 2004), effects on cycloheximide-induced amnesia (Hsieh et al. 1999), and inhibitory effects on human articular cartilage and chondrocytes (Choi et al. 2006a) that are exerted by SF. However, few studies have been conducted to evaluate the effects of SF on airway-related diseases. Therefore, we evaluated the effects of SF on asthma while focusing on its ability to recruit eosinophils.