An anticomplement homogeneous polysaccharide from the leaves of Rhododendron dauricum alleviates H1N1-induced pneumonia by reducing neutrophil extracellular trap formation.

Abstract

ETHNOPHARMACOLOGICAL RELEVANCE: Rhododendron dauricum L. leaves (RDL) are used in traditional Chinese medicine as a heat-clearing herb for pulmonary diseases. Our previous research suggested its anticomplement polysaccharides might help alleviate pneumonia, but their in vivo effects remain unreported. AIM OF THE STUDY: To obtain a homogeneous polysaccharide from RDL and investigate its anti-pneumonia effects and mechanisms. MATERIALS AND METHODS: DEAE-52 cellulose and gel permeation chromatography, methylation, and NMR analysis were used to isolate and characterize the homogeneous polysaccharide. Its in vitro anticomplement activity was determined by a hemolytic test. The therapeutic effect and mechanisms on pneumonia were evaluated in H1N1-infected mice. ELISA, immunohistochemistry, immunofluorescence, and Western blot were used to assess inflammatory markers, complement components, neutrophil recruitment, NET formation, and alveolar fluid clearance. Additionally, an H1N1-MRSA co-infection model was established to assess the efficacy of RDLP against dual infections. RESULTS: RDLP, a homogeneous branched acidic heteropolysaccharide (385.4 kDa), was isolated from RDL. It was mainly composed of arabinose, galactose and rhamnose, and showed significant anticomplement activity in vitro (CH = 24.99 ± 1.98 μg/mL). In vivo, RDLP alleviated H1N1-induced pneumonia by reducing lung injury, lung index, weight loss, and inflammatory marker levels. Mechanistically, it inhibited complement over-activation, suppressed neutrophil infiltration and NET formation, and promoted alveolar fluid clearance. RDLP also alleviated pneumonia in H1N1-MRSA co-infection. CONCLUSION: RDLP alleviated H1N1-induced pneumonia by inhibiting complement activation and reducing NET formation, highlighting its potential as a candidate for pneumonia treatment.