Laboratory of Chemical Glycobiology and ‡Experimental Animal Facility, National Institute of Immunology , Aruna Asaf Ali Marg, New Delhi 110067, India.
J Am Chem Soc. 2017 Jan 18;139(2):693-700. doi: 10.1021/jacs.6b08894. Epub 2017 Jan 5.
Sialic acids are abundant in the central nervous system (CNS) and are essential for brain development, learning, and memory. Dysregulation in biosynthesis of sialo-glycoconjugates is known to be associated with neurological disorders, CNS injury, and brain cancer. Metabolic glycan engineering (MGE) and bioorthogonal ligation have enabled study of biological roles of glycans in vivo; however, direct investigations of sialoglycans in brain have been intractable. We report a simple strategy utilizing carbohydrate-neuroactive hybrid (CNH) molecules, which exploit carrier-mediated transport systems available at the blood-brain barrier, to access brain via tail vein injection in mice. Peracetylated N-azidoacetyl-d-mannosamine (AcManNAz) conjugated with neuroactive carriers, namely, nicotinic acid, valproic acid, theophylline-7-acetic acid, and choline, were synthesized and evaluated in SH-SY5Y (human neuroblastoma) cells for MGE. Intravenous administration of CNH molecules in mice (C57BL/6J and BALB/cByJ) resulted in robust expression of N-azidoacetyl-neuraminic acid (NeuAz)-carrying glycoproteins in both brain and heart, while the nonhybrid molecule AcManNAz showed NeuAz expression in heart but not in brain. Successful neuroactive carriers were then conjugated with N-butanoyl-d-mannosamine (ManNBut) with a goal to achieve modulation of polysialic acid (polySia) on neural cell adhesion molecules (NCAM). PolySia levels on NCAM in adult mice were reduced significantly upon administration of AcManNBut-nicotinate hybrid, but not with AcManNBut. This novel application of MGE not only offers a noninvasive tool for investigating brain glycosylation, which could be developed in to brain mapping applications, but also serves as a potential drug by which modulation of neural glycan biosynthesis and thus function can be achieved in vivo.
唾液酸在中枢神经系统（CNS）中含量丰富，对大脑发育、学习和记忆至关重要。已知唾液酸糖缀合物生物合成的失调与神经紊乱、中枢神经系统损伤和脑癌有关。代谢糖工程（MGE）和生物正交连接已使人们能够在体内研究聚糖的生物学作用；然而，对大脑中唾液酸的直接研究一直难以实现。我们报告了一种利用碳水化合物-神经活性杂合体（CNH）分子的简单策略，该策略利用血脑屏障上可用的载体介导转运系统，通过尾静脉注射将其递送到小鼠的大脑中。合成了带有神经活性载体的乙酰化 N-叠氮乙酰基-d-甘露糖胺（AcManNAz）缀合物，即烟酸、丙戊酸、茶碱-7-乙酸和胆碱，并在 SH-SY5Y（人神经母细胞瘤）细胞中评估了它们在 MGE 中的作用。在 C57BL/6J 和 BALB/cByJ 小鼠中静脉内给予 CNH 分子，导致 NeuAz 携带糖蛋白在大脑和心脏中均有强烈表达，而非杂合体分子 AcManNAz 仅在心脏中而不在大脑中表达 NeuAz。然后，成功的神经活性载体与 N-丁酰基-d-甘露糖胺（ManNBut）缀合，目的是调节神经细胞黏附分子（NCAM）上的多唾液酸（polySia）。在成年小鼠中，给予 AcManNBut-烟酸杂合体后，NCAM 上的 polySia 水平显著降低，但给予 AcManNBut 则没有。这种 MGE 的新应用不仅为研究大脑糖基化提供了一种非侵入性工具，该工具可以进一步开发为大脑映射应用，而且还可以作为一种潜在的药物，通过调节神经聚糖的生物合成从而实现体内功能的调节。
