Structural characterization and immunomodulatory activity of a novel pectin polysaccharide extracted from Gardenia jasminoides fruit.

Gardenia jasminoides Ellis is an important medicinal and edible resource. However, the structure-activity relationships underlying the immunomodulatory activity of its polysaccharides remain incompletely understood. Herein, we aimed to characterize the structure of a novel pectin from Gardenia fruit and clarify its immunomodulatory mechanism. A homogeneous polysaccharide, GJP70-0.2 (M = 54.5 kDa), was isolated and purified from gardenia fruit. Structural analysis confirmed that it was a pectic polysaccharide characterized by a notably homogalacturonan (HG)-dominant architecture with minor rhamnogalacturonan-I (RG-I) domains. The main chain structure contains α-D-GalpA-(1→[4)-α-GalpA-6R-(1]→[3,4)-α-GalpA-(1]→[2,4)-α-Rhap-(1→4)-α-GalpA(1→], and the RG-I region harbors arabinan and type II arabinogalactan side chains. In vitro assays showed that GJP70-0.2 significantly enhanced RAW264.7 macrophage proliferation and phagocytic activity, and induced M1 polarization, as evidenced by increased nitric oxide (NO) and reactive oxygen species (ROS) secretion, as well as upregulated inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) expression. Mechanistically, GJP70-0.2 promoted M1 polarization by activating the NF-κB, JAK/STAT, and MAPK signaling pathways. Thus, the HG domain-dominant gardenia pectin polysaccharides exhibit potent immunomodulatory activities, supporting the potential of gardenia pectin polysaccharides as natural immunomodulators.