Hydrothermal processing of β-glucan from Aureobasidium pullulans produces a low molecular weight reagent that regulates inflammatory responses induced by TLR ligands

Abstract

The Kururu no β-glu® (KBG) is a commercial hydrothermal-treated Aureobasidium pullulans β-glucan produced by a unique hydrothermal process that results in high solubility of the β-glucan. In this study, we examined the biological activities of this reagent. RAW264.7 cells do not express Dictin-1 on the cell surface, but cells still respond to various pathogen molecular patterns. Lipopolysaccharide (LPS) induced nitrogen oxide (NO) synthesis and TNF−α production in RAW264.7 cells, and those were suppressed by KBG in a dose-dependent manner. The major signaling cell surface receptor respond to LPS is the TLR4/MD-2 complex. The UT12 antibody against to the TLR4/MD-2 complex mimics LPS function and induces cell responses. NO generation and TNF-α production were similarly induced in cells by stimulation with the antibody, but those were not suppressed by KBG. Cell responses induced by other TLR ligands, such as CPG (TLR9 ligand) and Pam3CSK4 (TLR1/TLR2 ligand), were also suppressed by KBG. Therefore, the target molecule for KBG is different from TLR receptors and Dictin-1. Although we also examined the suppressive activities of several other β-glucan products, comparable activities were not detected with other reagents. A unique hydrothermal process may produce the active reagent. Reprocessing KBG increased low molecular weight fractions, and suppressive activities were markedly enhanced. Therefore, low molecular weight fractions obtained by hydrothermal processing of KBG may result in potential reagents that control inflammation induced by various pathogens.