Ultrasonic Extraction Process of Polysaccharides from Dendrobium nobile Lindl.: Optimization, Physicochemical Properties and Anti-Inflammatory Activity

To optimize the ultrasonic extraction process of polysaccharides from Dendrobium nobile Lindl. (DNP), the extraction method was conducted through a single-factor test and the response-surface methodology (RSM). With the optimal extraction process (liquid–solid ratio of 40 mL/g, ultrasonic time of 30 min, and ultrasonic power of 400 W), the maximum extraction yield was 5.16 ± 0.41%. DNP1 and DNP2 were then fractionated via DEAE-QFF and Sephacryl S-300 HR chromatography. The molecular weight (Mw) of DNP1 was identified as 67.72 kDa, composed of Man (75.86 ± 0.05%) and Glc (24.14 ± 0.05%), and the Mw of DNP2 was 37.45 kDa, composed of Man (72.32 ± 0.03%) and Glc (27.68 ± 0.03%). Anti-inflammatory assays results showed that as DNPs were 200 μg/mL, and the contents of NO, TNF-α, IL-1β, IL-6 and IL-10 in LPS-induced RAW 264.7 cells were about 13.39% and 13.39%, 43.88% and 43.51%, 17.80% and 15.37%, 13.84% and 20.66%, and 938.85% and 907.77% of those in control group, respectively. It was indicated that DNP1 and DNP2 inhibited the inflammatory response of RAW 264.7 cells induced by LPS via suppressing the level of NO and pro-inflammatory cytokines (TNF-α, IL-1β and IL-6) and promoting the secretion of anti-inflammatory cytokine (IL-10). Therefore, DNP1 and DNP2 have potential applications in the treatment of inflammatory injury.