Abstract:
Naturally occurring complex carbohydrates represent a structurally diverse group
of macromolecules which shows a broad range of biological activities. However,
their clinical contribution is still limited because of the structural complexity, lack
of studies on structure activity relationship and underlying mechanisms of
biological activity of individual polysaccharide components. In the present study
polysaccharides were isolated from the cold-water extracts of two mushroom
species, Antrodia cinnamomea and Auricularia auricula-juadae, to investigate their
immunostimulatory potential and mechanisms of action. Polysaccharides were
purified by size exclusion and ion exchange chromatography and their chemical
structures were elucidated by Gas Chromatography-Mass Spectroscopy (GC-MS)
and Nuclear Magnetic Resonance Spectroscopy (NMR). Immunostimulatory
properties of each polysaccharide were investigated targeting the proinflammatory
cytokines (TNF-, IL-6) and nitric oxide (NO) producing abilities in selected
immune cell models (J774.1A and Raw 264.7). Immunologically active
polysaccharide of A. cinnamomea (ACP; MW>70 kDa) was chemically identified as
galactomannan, with branched octasaccharide repeating units, whereas
polysaccharide of A. auricula-ju dae (AAPS, MW>70 kDa) was identified as
glucuronoxylomannan with a heptasaccharide repeating units. O-acetyl
modification at mannose and xylose residues was observed in AAPS while
glucuronic acid residues remained unacetylated. Both ACP and native AAPS
activated murine macrophage cells to produce TNF- and IL-6 in a concentration
dependent manner. Toll like receptor 4 was identified as the main receptor involved
in ACP and AAPS mediated macrophage activation. Complete abrogation of
immunostimulatory properties was observed in deacetylated and carboxyl reduced
AAPS indicating the essentiality of both acetyl and carboxylic functionalities in
immunostimulatory process. Molecular modelling data further demonstrated the
role of acetyl and caroboxyl moieties in receptor binding. Our findings have
provided firm scientific evidences for the immunoenhancing properties of two
mushroom species and the potential of these two polysaccharides to be strong
candidates for the development of new carbohydrate-based nutraceutical
supplements and adjuvants in the treatment of immunity related disorders in near
future.
