Structural Features of Three Hetero-Galacturonans from Passiflora foetida Fruits and Their in Vitro Immunomodulatory Effects
Ya Song, Peng Wen, Huili Hao, Minqian Zhu, Yuanming Sun, Yuxiao Zou, Teresa Requena, Riming Huang, Hong Wang
Abstract
Passiflora foetida is a horticultural plant and vital traditional Chinese herbal medicine. In our previous study, the characterization and immuno-enhancing effect of fruits polysaccharide 1 (PFP1), a water-eluted hetero-mannan from wild Passiflora foetida fruits, were investigated. Herein, another three salt-eluted novel polysaccharides, namely PFP2, PFP3, and PFP4, were obtained and structurally characterized. The results showed that PFP2, PFP3, and PFP4 were three structurally similar hetero-galacturonans with different molecular weights of 6.11 × 104, 4.37 × 104, and 3.48 × 105 g/mol, respectively. All three of these hetero-galacturonans are mainly composed of galacturonic acid, galactose, arabinose (75.69%, 80.39%, and 74.30%, respectively), and other monosaccharides including mannose, fucose, glucose, ribose, xylose, and glucuronic acid (24.31%, 19.61, and 25.70%, respectively), although differences in their backbone structure exist. Additionally, immunomodulatory assay indicated that the three hetero-galacturonans possess the ability to promote the production of nitric oxide (NO), tumor necrosis factor-α (TNF-α), and interleukin-6 (IL-6) in RAW264.7 macrophages in a concentration-dependent manner (p < 0.05). Especially, PFP3 displayed a stronger enhancing effect than PFP2 and PFP4 at the minimum effective concentration. Therefore, the results suggested that the obtained three salt-eluted hetero-galacturonans, especially PFP3, could be utilized as immunomodulatory effectivity ingredients in nutritional/pharmaceutical industries.