Isolation of polysaccharides from Dendrobium officinale leaves and anti-inflammatory activity in LPS-stimulated THP-1 cells

Dendrobium officinale stem is rich in polysaccharides, which play a great role in the medicinal effects of this plant. However, little was known about the polysaccharides from Dendrobium officinale leaves. Two kinds of polysaccharides in the leaves, DLP-1 and DLP-2, were obtained by hot water extraction, alcohol sedimentation and chromatographic separation (DEAE-52 cellulose column and Sephadex G-100 column). The average molecular weights were determined as 28,342 Da and 41,143 Da, respectively. Monosaccharide compositions were analyzed using gas chromatography–mass spectrometer. DLP-1 was composed of d-(+)-galactose, dl-arabinose, and l-(+)-rhamnose with a molar ratio of 3.21:1.11:0.23, and traces of d-xylose, d-glucose, and d-(+)-mannose. DLP-2 was consisted of d-glucose and d-(+)-galactose with a molar ratio of 3.23:1.02, and traces of d-xylose, dl-arabinose. Then, we established inflammatory cell model by LPS acting THP-1 cells to investigate the anti-inflammatory effects of DLP-1 and DLP-2. The results indicated that DLP-1 (5 μg/mL) and DLP-2 (50 μg/mL) were effective in protecting THP-1 cells from LPS-stimulated cytotoxicity, as well as inhibiting reactive oxygen species formation. In addition, both DLP-1 (5 μg/mL) and DLP-2 (50 μg/mL) significantly suppressed toll-like receptor-4 (TLR-4), myeloid differentiation factor (MyD88) and tumour necrosis factor receptor-associated factor-6 (TRAF-6) mRNA and protein expression in LPS-stimulated THP-1 cells.