Structural Characteristics of Polysaccharide GP2a in Gardenia jasminoides and Its Immunomodulatory Effect on Macrophages

Here, we elucidated the structural characteristics of a polysaccharide isolated from Gardenia jasminoides Ellis (labeled as GP2a) and its immunomodulatory activity. GP2a is an acidic polysaccharide with a molecular weight of 44.8 kDa, mostly comprising galacturonic acid. Methylation analysis revealed 4-GalpA (74.8%) to be the major sugar residue in GP2a. Nuclear magnetic resonance analysis indicated that its main chain comprised -> 4)-alpha-D-GalpA-6-OMe-(1 -> 4)-alpha-D-GalpA-(1 -> and -> 4)-alpha-D-GalpA-6-OMe-(1 -> 2)-alpha-L-Rhap-(1 ->, with galactan and arabinans linked to the C-4 position of -> 2)-alpha-L-Rhap-(1 -> residue as branched chains. Furthermore, GP2a showed no obvious toxicity to macrophages (RAW 264.7) while enhancing cell viability in a dose- and time-dependent manner. Compared with untreated cells, nitric oxide production and secretion of cytokines, such as tumor necrosis factor-alpha, interferon-gamma, interleukin (IL)-1 beta, IL-6, and granulocyte macrophage colony stimulating factor, in GP2a-treated cells significantly increased after 48 h. At 300 mu g/mL GP2a concentration, there was no significant difference in the cytokine levels in GP2a- and lipopolysaccharide-treated cells (the positive control). In summary, GP2a is a pectic polysaccharide with homogalacturonan and rhamnogalacturonan-I structural regions in the main chain. Based on its immunomodulatory effects in vitro, GP2a may have potential uses in functional food and medicine.

Automated summary

We characterized the structure and immunomodulatory activity of a polysaccharide (GP2a) isolated from Gardenia jasminoides Ellis. GP2a is an acidic polysaccharide mostly composed of galacturonic acid residues, with homogalacturonan and rhamnogalacturonan-I regions in the main chain. GP2a showed no toxicity to macrophages and enhanced cell viability. It also increased the production and secretion of various cytokines.