A novel flavonol-polysaccharide from Tamarix chinensis alleviates influenza A virus-induced acute lung injury. Evidences for its mechanism of action

Tamarix chinensis Lour. is a Chinese medicine used for treating inflammation-related diseases and its crude polysaccharides (MBAP90) exhibited significant anticomplement activities in vitro. To obtain anticomplement homogenous polysaccharides from MBAP90 and explore its therapeutic effects and potential mechanism on influenza A virus (IAV)-induced acute lung injury (ALI). Anticomplement activity-guided fractionation of the water-soluble crude polysaccharides from the leaves and twigs of T. chinensis were performed by diethylaminoethyl-52 (DEAE-52) cellulose and gel permeation columns to yield a homogeneous polysaccharide MBAP-5, which was further characterized using ultra-high-performance liquid chromatography-ion trap tandem mass spectrometry (UPLC-IT-MS) and nuclear magnetic resonance (NMR) analysis. In vitro, the anticomplement activity of MBAP-5 through classical pathway was measured using a hemolytic test. The therapeutic effects of MBAP-5 on ALI were evaluated in H1N1-infected mice. H&E staining, enzyme linked immunosorbent assay (ELISA), immunohistochemistry, and western blot were used to systematically access lung histomorphology, inflammatory cytokines, degree of complement component 3c, 5aR, and 5b-9 (C3c, C5aR, and C5b-9) deposition, and inflammasome signaling pathway protein expressions in lung tissues. MBAP-5 was a novel flavonol-polysaccharide with the molecular weight (Mw) of 153.6 kDa. Its structure was characterized to process a backbone of →4)-α-D-GlcpA-(1→, →6)-α-D-Glcp-(1→, →3,4)-α-D-Glcp-(1→, →3,4,6)-α-D-Glcp-(1→, and →4,6)-β-D-Glcp-(1→, as well as branches of α-L-Araf-(1→ and β-D-Galp-(1→. Particularly, O-3 of →3,4,6)-α-D-Glcp-(1→ was substituted by quercetin. In vitro assay showed that MBAP-5 had a potent anticomplement activity with a CH50 value of 102 ± 4 µg/ml. Oral administration of MBAP-5 (50 and 100 mg/kg) effectively attenuated the H1N1-induced pulmonary injury in vivo by reducing pulmonary edema, virus replication, and inflammatory responses. Mechanistically, MBAP-5 inhibited the striking deposition and contents of complement activation products (C3c, C5aR, and C5b-9) in the lung. Toll-like receptor 4 (TLR4) /transcription factor nuclear factor κB (NF-κB) signaling pathway was constrained by MBAP-5 treatment. In addition, MBAP-5 could suppress activation of the inflammasome pathways, including Nod‐like receptor pyrin domain 3 (NLRP3), cysteinyl aspartate specific proteinase-1/12 (caspase-1/12), apoptosis‑associated speck‑like protein (ASC), gasdermin D (GSDMD), interleukin (IL)-1β, and IL-18 expressions. A novel flavonol-polysaccharide MBAP-5 isolated from T. chinensis demonstrated a therapeutic effect against ALI induced by IAV attack. The mechanism might be associated with inhibition of complement system and inflammasome pathways activation.