Structural Identification and Anti-Neuroinflammatory Effects of a Pectin–arabinoglucuronogalactan Complex, AOPB-1-1, Isolated from Asparagus Officinalis

Asparagus officinalis L. is a horticultural crop that contains a variety of bioactive compounds with antiinflammatory effects. Aqueous extracts of A. officinalis can noticeably improve the learning and memory function of model mice. Herein, a pectin-arabinoglucuronogalactan complex (AOPB-1-1) with a relative molecular weight of 90.8 kDa was isolated from A. officinalis. The repeating structural unit of AOPB-1-1 was identified through monosaccharide composition, methylation analysis, uronic acid reduction, partial acid hydrolysis, and nuclear magnetic resonance spectroscopy. AOPB-1-1 contains the rhamnogalacturonan-I (RG-I) domain of pectin polysaccharides (PPs) and arabinoglucuronogalactan (AGG) regions. The backbone of the AGG region is composed of -> 3,6)-beta-D-Galp-(1 -> and -> 4)-beta-D-Glcp-(1 -> residues substituted at the 4-position to the -> 4)-alpha-DGalAp-(1 -> residues of the RG-I main chain. The anti-neuroinflammatory activity of AOPB-1-1 suggests that it can significantly reduce the content of inflammatory cytokines, including nitric oxide (NO), tumor necrosis factor-alpha (TNF-alpha), and interleukin-6 (IL-6) and inhibit the expression of inflammatory genes including cyclooxygenase-2 (COX2), nitric oxide synthase (iNOS), TNF-alpha, IL-6, and interleukin-1 beta (IL-1 beta) in LPS-stimulated BV2 cells. Furthermore, its inhibitory effects on TNF-alpha and IL-6 levels were even better than those of minocycline. The significant anti-neuroinflammatory activity of AOPB-1-1 suggests its applicability as a therapeutic option for the treatment of Alzheimer's disease.