Cordysinocan, a polysaccharide isolated from cultured Cordyceps, activates immune responses in cultured T-lymphocytes and macrophages: Signaling cascade and induction of cytokines

Abstract

Cordyceps sinensis, a well-known traditional Chinese medicine, possesses activities in anti-tumor, anti-oxidation and stimulating the immune response; however, the identity of active component(s) is not determined. A strain of Cordyceps sinensis, namely UST 2000, has been isolated. By using activity-guided purification, a novel polysaccharide of molecular weight ∼82 kDa was isolated from the conditioned medium of cultured Cordyceps. The isolated exo-polysaccharide, namely cordysinocan, contains glucose, mannose, galactose in a ratio of 2.4:2:1. In cultured T-lymphocytes, application of cordysinocan induced the cell proliferation and the secretion of interleukin-2, interleukin-6 and interleukin-8. In addition, the phosphorylation of extracellular signal-regulated kinases (ERK) was induced transiently by the treatment of cordysinocan. Moreover, application of cordysinocan in cultured macrophages increased the phagocytosis activity and the enzymatic activity of acid phosphatase. These results therefore verify the important role of Cordyceps polysaccharide in triggering such immune responses.

Introduction

Cordyceps, one of the most valued traditional Chinese medicines, consists of the dried fungus Cordyceps sinensis growing on the larva of caterpillar. It is also known as “summer-grass and winter worm” because of its appearance during different seasons. The parasitic complex of the fungus and the caterpillar are found in the soil of a prairie at an elevation of 3500–5000 m. According to Chinese medicinal theory, Cordyceps processes both “Yin-nourishing” and “Yang-invigorating” activities (Siu et al., 2004). Indeed, different therapeutic purposes of Cordyceps have been reported, which include stimulation of immune response; inhibition of cancer growth; protection of kidney and liver; stimulation of cardiovascular circulation; lowering blood glucose; and against free-radical formation (Zhu et al., 1998a, Zhu et al., 1998b, Li and Tsim, 2004).

Nucleoside and polysaccharide are often closely associated with the pharmacological activities of Cordyceps. Cordyceps contains a high concentration of adenosine, guanosine and uridine (Zhu et al., 1998a, Zhu et al., 1998b, Li et al., 2001a, Li et al., 2001b), while adenosine is believed to play a key role in the pharmacological effects of Cordyceps (Chen et al., 1997). Although polysaccharide is well documented to be a major active ingredient of Cordyceps, ranging from 3 to 8% of its total dry weight (Li et al., 2003), the structure and function of which have not been fully revealed. Amongst different functions of Cordyceps polysaccharides, a polysaccharide-enriched fraction was isolated from cultured Cordyceps, which processed anti-oxidation activities (Li et al., 2001a). To account for the anti-cancer effect, a Cordyceps polysaccharide fraction was shown to have significantly inhibition effect on the proliferation of a human leukemic monocyte lymphoma U937 cells (Chen et al., 1997). In the immune responses, an exo-polysaccharide was identified from cultured Cordyceps, and which was found to induce the production of tumor necrosis factor-alpha (TNF-α), interleukin (IL)-6, and IL-10 in human peripheral blood (Kuo et al., 2007).

In searching for bioactive compound(s) from Cordyceps, we employed a method of activity-guided purification approach to isolate an exo-polysaccharide from the cultured Cordyceps. This exo-polysaccharide has a molecular weight of ∼82 kDa, namely cordysinocan, and which possesses strong immuno-stimulating activities in both cultured T-lymphocyte and macrophage. In addition, the downstream signaling of cordysinocan-mediated immune response was revealed here.