Category: Oligonucleotide/oligosaccharide conjugates

GM1 Oligosaccharide Crosses the Human Blood–Brain Barrier In Vitro by a Paracellular Route

No Comments Ganglioside GM1 (GM1) has been reported to functionally recover degenerated nervous system in vitro and in vivo, but the possibility to translate GM1′s potential in clinical settings is counteracted by its low ability to overcome the blood–brain barrier (BBB) due to its amphiphilic nature. Interestingly, the soluble and hydrophilic GM1-oligosaccharide (OligoGM1) is able to punctually replace GM1 neurotrophic functions alone, both in vitro and in vivo. In order to take advantage of OligoGM1 properties, which overcome GM1′s pharmacological limitations, here we characterize the OligoGM1 brain transport by using a human in vitro BBB model. OligoGM1 showed a 20-fold higher crossing rate than GM1 and time–concentration-dependent transport. Additionally, OligoGM1 crossed the barrier at 4 °C and in inverse transport experiments, allowing consideration of the passive paracellular route. This was confirmed by the exclusion of a direct interaction with the active ATP-binding cassette (ABC) transporters using the “pump out” system. Finally, after barrier crossing, OligoGM1 remained intact and able to induce Neuro2a cell neuritogenesis by activating the TrkA pathway. Importantly, these in vitro data demonstrated that OligoGM1, lacking the hydrophobic ceramide, can advantageously cross the BBB in comparison with GM1, while maintaining its neuroproperties. This study has improved the knowledge about OligoGM1′s pharmacological potential, offering a tangible therapeutic strategy. (Int J Mol Sci. 2020 Apr; 21(8): 2858.)

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Nonenzymatic polymerase-like template-directed synthesis of acyclic l-threoninol nucleic acid

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Charleston Evolution of xeno nucleic acid (XNA) world essentially requires template-directed synthesis of XNA polymers. In this study, we demonstrate template-directed synthesis of an acyclic XNA, acyclic l-threoninol nucleic acid (l-aTNA), via chemical ligation mediated by N-cyanoimidazole. The ligation of an l-aTNA fragment on an l-aTNA template is significantly faster and occurs in considerably higher yield than DNA ligation. Both l-aTNA ligation on a DNA template and DNA ligation on an l-aTNA template are also observed. High efficiency ligation of trimer l-aTNA fragments to a template-bound primer is achieved. Furthermore, a pseudo primer extension reaction is demonstrated using a pool of random l-aTNA trimers as substrates. To the best of our knowledge, this is the first example of polymerase-like primer extension of XNA with all four nucleobases, generating phosphodiester bonding without any special modification. This technique paves the way for a genetic system of the l-aTNA world.

Why nature chose ribofuranosyl nucleic acids rather than some other family of molecular structure as the carrier of genetic material has prompted chemists to synthesize various xeno nucleic acids (XNAs) composed of unnatural scaffolds. Cyclic XNAs such as hexitol nucleic acid, cyclohexenyl nucleic acid, tricyclo-DNA, arabinonucleic acid, and (3′,2′)-α-L-threose nucleic acid (TNA) form homoduplexes and cross-pair with DNA and/or RNA. Due to the structural similarities to DNA and RNA, cyclic XNAs can be polymerized on a template using native and engineered polymerases, and functional XNAs that act as ribozymes and aptamers have been identified using in vitro selection. TNA has particularly attracted attention because it is chemically simpler than RNA and may have existed prior to RNA. Interestingly, a ring structure is not necessary for stable duplex formation. Several XNAs composed of acyclic structures have been synthesized. An example is glycerol nucleic acid (GNA), designed by the Zhang et al.. Although GNA does not have a ring structure, it forms very stable homoduplex and can cross-pair with RNA, depending on the sequence. As other examples, we have reported serinol nucleic acid and acyclic l-threoninol nucleic acid (l-aTNA), which can cross-hybridize with DNA and RNA and has high nuclease durability, promising application to wide variety of situations such as living cell system. Not only our group but Kumar, Gothelf, et al. Kumar et al., Kumar and Gothelf, and Kumar et al. have also reported unique properties of l-aTNA.

A condensing reagent N-cyanoimidazole (CNIm) can connect a phosphate with a neighboring hydroxyl group to generate a phosphodiester bond, the same type of bond formed with natural enzymatic ligation. For DNA, ligation of various types of structures were achieved using CNIm, due to relatively high reaction yields. Examinations of the concentration dependences on CNIm and Mn2+ showed that 20 mM CNIm and 20 mM Mn2+ were sufficient for effective ligation. We also determined yields in Cd2+, Co2+, Ni2+, and Zn2+ and showed that each of these metal ions could substitute for Mn2+. Thus, a wide variety of divalent metals induce ligation of l-aTNA. (Nat Commun. 2021; 12: 804.)

Introduction of 2,6-Diaminopurines into Serinol Nucleic Acid Improves Anti-miRNA Performance

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MicroRNAs (miRNAs) are endogenous small RNAs that regulate gene expression at the post-transcriptional level by sequence-specific hybridisation. Anti-miRNA oligonucleotides (AMOs) are inhibitors of miRNA activity. Chemical modification of AMOs is required to increase binding affinity and stability in serum and cells. In this study, we synthesised AMOs with our original acyclic nucleic acid, serinol nucleic acid (SNA), backbone and with the artificial nucleobase 2,6-diaminopurine. The AMO composed of only SNA had strong nuclease resistance and blocked endogenous miRNA activity. A significant improvement in anti-miRNA activity of the AMO was achieved by introduction of a 2,6-diaminopurine residues into the SNA backbone. In addition, we found that the enhancement in AMO activity depended on the position of the 2,6-diaminopurine residue in the sequence. The high potency of the SNA-AMOs suggests that these oligomers will be useful as therapeutic reagents for control of miRNA function in patients and as tools for investigating the roles of microRNAs in cells. (Chembiochem . 2017 Oct 5;18(19):1917-1922.)