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孢粉素的物理化学性质和生物医学应用研究进展*
Advances of the Physiochemical Properties of Sporopollenin and Its Biomedical Applications
({{custom_author.role_en}}), {{javascript:window.custom_author_en_index++;}}孢粉素是类聚乙烯醇链通过酯键和缩醛高度交联的天然生物高分子,构成花粉和孢子的外壁,能够抵抗物理、化学、生物腐蚀,堪称自然界最坚固的有机物,被誉为植物界的金刚石。孢粉素微囊(SEC)自然界来源丰富、生物相容性好、无免疫原性,表面含有丰富的羧基、羟基和酚基,能够功能化或者与其他纳米材料构建复合材料;其表面丰富的纳米孔道增加了材料的比表面积,有利于捕获癌细胞或目标生物分子。SEC独特的性质使其在药物载体、口服疫苗载体、影像诊断、生物传感、细胞生长支架、微反应器、微型机器人等方面得到广泛的应用。阐述了孢粉素的结构、物理化学性质、制备方法和功能化方面的研究进展, 探讨了孢粉素的应用前景、存在的问题以及未来的发展方向。
Sporopollenin (SP) is a highly cross-linked natural biopolymer composed of polyvinyl alcohol-like unit crosslinked through ester and acetal linkage. SP forms the outer wall of pollen and spore and can resist physical, chemical and biological corrosion. It is the most robust organic compound in nature and is known as the diamond of plant kingdom. Sporopollenin exine capsules (SEC) are abundant in nature. They have good biocompatibility and no immunity. The rich carboxyl, hydroxyl and phenolic groups make SEC easy to be functionalized or complexed with nanomaterials. The plentiful nanochannels on SEC increases their specific surface area, supporting capture of cancer cell and biomolecules. The unique properties of SEC lead to their wide applications in drug delivery carriers, oral vaccine carriers, medical imaging, biosensing, cell growth scaffold, microreactor, micro robot, etc. In this review, the physicochemical properties, preparation methods and functionalization of SP as well as the research progress of SEC are discussed. The application prospect, existing problems and future development direction of SEC are summarized.
孢粉素 / 花粉 / 孢子 / 微囊 / 药物载体 {{custom_keyword}} /
Sporopollenin / Pollen / Spore / Microcapsule / Drug carrier {{custom_keyword}} /
图4 孢粉素微囊在生物医学中的应用Fig.4 Application of sporopollenin microcapsule in biomedicine (a) Optical image of DOX-loaded Pt-pollen microrobots[22] (b) Fluorescence image of DOX-loaded Pt-pollen microrobots[22] (c) Cell viability results of MCF-7 cells for DOX-loaded Pt-pollen microrobots[22] (d) In vitro release of BSA[14] (e) Release of the gadolinium contrast agent[30] |
图6 孢粉素微囊捕获癌细胞Fig.6 Capture of cancer cells using sporopollenin exine capsule (a) TEM image of a captured MCF-7 cell on EChry film (b) Schematic illustration of the filopodia of cancer cell stuck into the nanocage (c) The number of MCF-7 cells captured on EChry film as a function of loaded cell number (d) Capture yields of various cancer cells on EChry film[40] |
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Pollen grain and spore shells are natural microcapsules designed to protect the genetic material of the plant from external damage. The shell is made up of two layers, the inner layer (intine), made largely of cellulose, and the outer layer (exine), composed mainly of sporopollenin. The relative proportion of each varies according to the plant species. The structure of sporopollenin has not been fully characterised but different studies suggest the presence of conjugated phenols, which provide antioxidant properties to the microcapsule and UV (ultraviolet) protection to the material inside it. These microcapsule shells have many advantageous properties, such as homogeneity in size, resilience to both alkalis and acids, and the ability to withstand temperatures up to 250 °C. These hollow microcapsules have the ability to encapsulate and release actives in a controlled manner. Their mucoadhesion to intestinal tissues may contribute to the extended contact of the sporopollenin with the intestinal mucosa leading to an increased efficiency of delivery of nutraceuticals and drugs. The hollow microcapsules can be filled with a solution of the active or active in a liquid form by simply mixing both together, and in some cases operating a vacuum. The active payload can be released in the human body depending on pressure on the microcapsule, solubility and/or pH factors. Active release can be controlled by adding a coating on the shell, or co-encapsulation with the active inside the shell.
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Sporopollenin exine capsules (SEC) extracted from Lycopodium clavatum spores were shown to encapsulate ibuprofen as a drug model, with 97 ± 1% efficiency as measured by recovery of the loaded drug and absence of the drug on the SEC surface by scanning electron microscopy (SEM). The encapsulated ibuprofen was shown to be unchanged from its bulk crystalline form by solid state NMR, FTIR and XRD. Essential for drug delivery applications, SEC were shown to be non-toxic to human endothelial cells and free of allergenic protein epitopes by MALDI-TOF-MS and ESI-QqToF-MS. Potential application for targeted release into the intestinal region of the gastrointestinal tract (GIT) was demonstrated by 88 ± 1% of the drug being retained in simulated gastric fluid (SGF) after 45 minutes and 85 ± 2% being released after 5 min in buffer (PBS; pH 7.4). The SEC were shown to provide significant taste masking of encapsulated ibuprofen in a double blind trial with 10 human volunteers.
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Two-level delivery systems (DSs) for oral administration of therapeutic proteins and peptides were developed. The first level consists of outer walls of Lycopodium clavatum spores (sporopollenin exine capsules, SECs) with included target objects; the alginate microgranules serve as the second (outer) level. Alginate (a pH-dependent natural polymer) protects peptides from gastric acidity and enzyme exposure and provides slow release of target objects in an alkaline intestinal medium. Introducing ovomucoid (a peptidase inhibitor) into alginate coatings prevents enzymatic hydrolysis of peptide objects in the intestinal medium. The elemental composition of spores and SECs was controlled using energy-dispersion spectroscopy and combustion analysis; their morphology was visualized by SEM. The efficiencies of different methods of SEC loading were compared. It was demonstrated that the load value was controlled by molecular mass and the value of the isoelectric point of target objects. A comparison of peptide in vitro release profiles from DSs of various structures into simulated gastric and intestinal fluids was carried out. The mechanism of peptide release from two-level DSs was suggested. SECs were found in rat blood after intragastric administration of the two-level DSs. Time profiles of therapeutic peptide release were obtained in vivo.
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