Panax ginseng has a 5000-year-long history as a traditional herbal medicine in Eastern Asia and North America. It is also known as crown jewel in traditional Chinese herbs because of its wide pharmacological properties. Ginsenosides, a class of saponins containing triterpene aglycones and various sugar moieties, are the main active components of ginseng. Considering the low abundance of ginsenosides and other abundant interferences, separation of ginsenosides is essential prior to further analysis. Recently, our group demonstrated the potential of a boronate affinity material for the selective enrichment of ginsenosides. However, conventional boronate affinity materials suffer from an apparent drawback. The binding strength of boronic acids toward cis-diol-containing compounds is low, with dissociation constants (Kd) ranging from 10-1 to 10-3mol/L. Thus, it is necessary to develop boronate affinity materials with high binding strength. In this study, we developed polyethyleneimine (PEI)-functionalized boronate affinity magnetic nanoparticles (BA-MNPs) for the selective enrichment of ginsenosides. Branched PEI was applied as a scaffold to amplify the number of boronic acid moieties, while 3-formylphenylboronic acid, which shows high affinity toward cis-diol-containing molecules, was used as the affinity ligand. In addition, the presence of the multi-glycan structure of ginsenoside leads to higher binding affinity between the PEI-BA-MNPs due to the synergistic multivalent binding effect. Combining with high performance liquid chromatography, a method for the selective analysis of ginsenosides was established. With ginsenoside Re as the representative and under the optimized conditions for magnetic solid-phase extraction, the developed method showed good linearity in the range of 50-800 μg/L, with a linear correlation coefficient (R2) of 0.9681. At different spiked levels (0.1-10 mg/L), the recoveries were in the range of 91.5%-117.3%, and the relative standard deviations (RSDs) ranged from 7.2% to 13.4%. Since the PEI-BA-MNPs exhibited significantly improved binding strength toward ginsenosides, they could extract trace glycoproteins. After enrichment, a 50-fold improvement in the sensitivity was achieved. In addition, the PEI-BA-MNPs maintained at least 72% of their original binding capacity after five consecutive uses. Finally, the developed method was applied to the determination of ginsenoside Re in commercial medicine (Qipi oral liquid). As opposed to the tedious and time-consuming sample preparation in the standard method (Pharmacopoeia of the People's Republic of China, 2015; ChP2015), the present protocol allowed for direct enrichment of the diluted commercial medicine with PEI-BA-MNPs. The magnetic separation made the overall experiment much simpler than the standard ChP2015 method. After washing and elution, the enriched ginsenoside Re was eluted and subjected to HPLC-UV analysis. The results obtained with the developed method (0.27%) were similar to those of ChP2015 (0.31%). We have experimentally demonstrated that PEI-BA-MNPs are ideal affinity sorbents for the selective enrichment of ginsenosides owing to their significant advantages, including high affinity, excellent selectivity, easy manipulation, high binding capacity, and fast binding equilibrium. As many saponins contain sugar side chains, we foresee a promising prospect for the proposed method in real-world applications.
为了实现更高效的人参皂苷富集,以硼亲和色谱为核心,结合支链聚乙烯亚胺放大硼酸配基数量,合成了支链聚乙烯亚胺辅助硼酸功能化磁性纳米粒(PEI-BA-MNPs),用于实际样品中人参皂苷的选择性富集,结合高效液相色谱,建立了一种分析实际样品中的人参皂苷的方法。以人参皂苷Re为代表,在优化的磁性固相萃取的条件下,该方法在50~800 μg/L的范围内呈现良好的线性,线性相关系数(R2)为0.9681。添加水平在0.1~10 mg/L时,回收率为91.5%~117.3%,相对标准偏差为7.2%~13.4%。由于所得材料对于人参皂苷的高亲和力,经所建立的方法富集过后,人参皂苷Re的灵敏度提高了约50倍。同时,所得材料重复使用5次以后还可以保持至少72%的原始吸附量。最后,将该方法用于启脾口服液中人参皂苷Re的含量分析,并与2015版《中国药典》的标准方法做对比。结果显示,所建立的方法检测出的人参皂苷Re含量为0.27%,虽然与标准方法测得的含量(0.31%)有些微差距,但该法极大地节约了实际操作中样品前处理的步骤和时间。结果表明,所制得的PEI-BA-MNPs可以用作磁性固相萃取吸附剂实现实际样品中人参皂苷的选择性富集。该方法亲和力强,选择性好,灵敏度高,操作快速简便且准确度高,具有很大的应用价值和发展前景。
Keywords: boronate affinity; ginsenosides; high performance liquid chromatography (HPLC); magnetic nanoparticles; polyethyleneimine.