Structural characterization and anticomplement activity of an acidic polysaccharide containing 3-O-methyl galactose from Juniperus tibetica
Graphical abstract
Introduction
The complement system plays an important role in the body's immune system. This system can be activated by a cascade mechanism of classical pathway, alternative pathway or mannan binding lectin pathway [1,2]. When the system activated, its primary biological function is to recognize “foreign” particles and macromolecules, and to promote their elimination by lysis. But when activated excessively, the complement system may cause varieties of autoimmune related diseases, such as system lupus erythematosus, rheumatoid arthritis, pneumonia and acute respiratory distress syndrome [[3], [4], [5]]. Complement inhibitors can block the complement cascade and thus represent one strategy for treating these diseases.
Some polysaccharides from the heat-clearing Chinese medicine, such as Bupleurum chinense [6], Scutellaria barbata [7], Eucommia ulmoides [8,9] had exhibited in vitro anticomplement effects. Moreover, the therapeutic effects of these anticomplement polysaccharides on acute lung injury [[10], [11], [12], [13], [14]] and autoimmune disease such as systemic lupus erythematosus [15], lupus nephritis [16] had also been confirmed in vivo. The natural polysaccharides with anticomplement activity would be potential agents of complement inhibitors.
Juniperus tibetica Kom., as one of the origin plants of Tibetan medicine Xuba, has been traditionally used for the treatment of many diseases, such as rheumatic arthritis, pneumonia and furuncle in Tibet [17]. Our preliminary experiment had found that the crude polysaccharides of J. tibetica exhibited potent anticomplement activity (CH50 = 68.29 ± 7.67 μg/mL). However, few studies have investigated polysaccharides from J. tibetica.
Herein, we reported the isolation and structural characterization of a homogeneous polysaccharide from J. tibetica. The anticomplement activities of the polysaccharide against classical pathway and alternative pathway were also investigated, along with its targets in the complement activation cascade.
Section snippets
Materials and reagents
The twigs and leaves of J. tibetica were collected from Tibet in October 2014. The plant materials were verified by associate Prof. Ji De (College of Science, Tibet University), and the voucher specimen (ST2014) has been deposited at the Herbarium of Materia Medica, Department of Pharmacognosy, Fudan University. Packing material DEAE-52 and Sephacryl™ S-300 were purchased from GE Healthcare (Uppsala, Sweden). NaBH4, D2O, trifluoroacetic acid (TFA) and anhydrous DMSO were purchased from
Isolation and purification
The crude polysaccharides (140 g, yield: 4.8%) were extracted from the herb (3.0 kg) through boiling water extraction and ethanol precipitation. The crude polysaccharides (100 g) were fractionated through anion-exchange chromatography, and 1.6 M-EP-YB (0.8 g, yield: 0.08%) was obtained. The fraction was further purified through size-exclusion chromatography, thus obtaining the YB-PS4 (45 mg). The total sugar content of YB-PS4 was 96.69%. The uronic acid content in YB-PS4 was 20.34%. GPC-MALLS (
Conclusion
In this study, the polysaccharide YB-PS4 was extracted and purified from the twigs and leaves of Juniperus tibetica and its possible repetitive units were proposed and further confirmed by oligosaccharide analysis. The polysaccharide had a backbone composed of→2,4)-α-Rhap-(1→, →3,5)-α-Araf-(1→, →2,4)-α-Galp-(1→, and →4)-α-GalpA-(1→, with branches of →2)-α-Rhap-(1→, →3)-α-Araf-(1 → and →2)-3-O-Me-α-Galp-(1→. YB-PS4 exhibited significant anticomplement activity by blocking C1q, C2, C3, C4 and C5
Acknowledgement
This work was supported by grants from the National Natural Science Foundation of China (81673690, 81872977), the major project of Science and Technology of Tibet Autonomous Region, China (XZ201801-GH-13), the Ministry of Science and Technology of China (2018ZX09735003-002), and the Development Project of Shanghai Peak Disciplines-Integrative Medicine (20180101).
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