Wuxiao Ding

Functionalized organic nanotubes as tubular nonviral gene transfer vector

Tubular nanomaterials are expected to represent a novel nonviral gene transfer vectors due to the unique morphology and potential biological functionalities. Here we rationally constructed functionalized organic nanotubes (ONTs) for gene delivery through the co-assembly of bipolar glycolipid, arginine-lipid and PEG-lipid. The arginine- and PEG-functionalized ONTs efficiently formed complexes with plasmid DNA without aggregation, and protect DNA from enzymatic degradation; while the arginine-functionalized ONTs aggregated with DNA as large bundles. Long ONTs exceeding 1μm in length was rarely taken up into the cells, while those with a length of 400-800nm could effectively deliver plasmid DNA into cells and induce high transgene expression of green fluorescense protein. This study demonstrated the usefulness of functionalized ONT in gene delivery, and the functionalized ONT represents a novel type of tubular nonviral gene transfer vector.

Encapsulation of poorly water-soluble drugs into organic nanotubes for improving drug dissolution

Hydrocortisone (HC), a poorly water-soluble drug, was encapsulated within organic nanotubes (ONTs), which were formed via the self-assembly of N-{12-[(2-α,β-d-glucopyranosyl) carbamoyl]dodecanyl}-glycylglycylglycine acid. The stability of the ONTs was evaluated in ten organic solvents, of differing polarities, by field emission transmission electron microscopy. The ONTs maintained their stable tubular structure in the highly polar solvents, such as ethanol and acetone. Furthermore, solution-state (1)H-NMR spectroscopy confirmed that they were practically insoluble in acetone at 25°C (0.015 mg/mL). HC-loaded ONTs were prepared by solvent evaporation using acetone. A sample with a 3/7 weight ratio of HC/ONT was analyzed by powder X-ray diffraction, which confirmed the presence of a halo pattern and the absence of any crystalline HC peak. HC peak broadening, observed by solid-state (13)C-NMR measurements of the evaporated sample, indicated the absence of HC crystals. These results indicated that HC was successfully encapsulated in ONT as an amorphous state. Improvements of the HC dissolution rate were clearly observed in aqueous media at both pH 1.2 and 6.8, probably due to HC amorphization in the ONTs. Phenytoin, another poorly water-soluble drug, also showed significant dissolution improvement upon ONT encapsulation. Therefore, ONTs can serve as an alternative pharmaceutical excipient to enhance the bioavailability of poorly water-soluble drugs.

Cisplatin-encapsulated organic nanotubes by endo-complexation in the hollow cylinder.

A bipolar glycolipid self-assembles into organic nanotubes upon its chelation with an anticancer drug cis-dichlorodiamineplatinum(II) (CDDP). The facile synthesis of glycolipid, chelation-assisted formation of the nanotubes, and efficient loading and prolonged release of CDDP demonstrate a new approach to high-axial supramolecular drug nanocarriers.

Lipid Nanotube Tailored Fabrication of Uniquely Shaped Polydopamine Nanofibers as Photothermal Converters

Helically coiled and linear polydopamine (PDA) nanofibers were selectively fabricated with two different types of lipid nanotubes (LNTs) that acted as templates. The obtained coiled PDA-LNT hybrid showed morphological advantages such as higher light absorbance and photothermal conversion effect compared to a linear counterpart. Laser irradiation of the coiled PDA-LNT hybrid induced a morphological change and subsequent release of the encapsulated guest molecule. In cellular experiments, the coiled PDA-LNT efficiently eliminated HeLa cells because of its strong affinity with the tumor cells. This work illustrates the first approach to construct characteristic morphologies of PDA nanofibers using LNTs as simple templates, and the coiled PDA-LNT hybrid exhibits attractive photothermal features derived from its unique coiled shape.

Spontaneous Nematic Alignment of a Lipid Nanotube in Aqueous Solutions

The dispersibility and liquid crystal formation of a self-assembled lipid nanotube (LNT) was investigated in a variety of aqueous solutions. As the lipid component, we chose a bipolar lipid with glucose and tetraglycine headgroups, which self-assembled into an LNT with a small outer diameter of 16 to 17 nm and a high axial ratio of more than 310. The LNT gave a stable colloidal dispersion in its dilute solutions and showed spontaneous liquid crystal (LC) alignment at relatively low concentrations and in a pH region including neutral pH. The LNT samples with shorter length distributions were prepared by sonication, and the relationship between the LNT axial ratio and the minimum LC formation concentration was examined. The robustness of the LNT made the liquid crystal stable in mixed solvents of water/ethanol, water/acetone, and water/tetrahydrofuran (1:1 by volume) and at a temperature of up to 90 °C in water. The observed colloidal behavior of the LNT was compared to those of similar 1D nanostructures such as a phospholipid tubule.

Effects of PEGylation on the physicochemical properties and in vivo distribution of organic nanotubes

Application of organic nanotubes (ONTs) into drug nanocarriers ultimately requires validation in live animals. For improving the dispersibility in biological media and in vivo distribution, the outer surface of an ONT was functionalized with polyethylene glycol (PEG) via the coassembly of an ONT-forming lipid with 5–20 mol% of a PEG-tethered lipid analogue (PEG-lipid). Firstly, the effect of PEGylation on the psysicochemical properties of ONTs, such as morphology and dispersibility, was investigated. PEGylation of ONTs slightly reduced the average length and effectively prevented the aggregation in phosphate-buffered saline (PBS). The PEGylated ONTs even showed high thermal stability in aqueous dispersion at least up to 95°C. Secondly, differential scanning calorimetry and powder X-ray diffraction indicated that ~10 mol% of PEG-lipid was completely incorporated into the ONTs, while 20 mol% of PEG-lipid encountered a partial phase separation during coassembly. In the heating differential scanning calorimetry runs, the resultant PEGylated ONTs with 5 mol% PEG-lipid showed no sign of phase separation up to 180°C under lyophilized condition, while those with 10 mol% and 20 mol% PEG-lipid showed some phase separation of the PEG-lipid above 120°C. Finally, PEGylation significantly affected the tissue distribution and prolonged the persistence time in the blood in mice. Non-PEGylated ONTs was quickly cleared from the circulation after intravenous infusion and preferentially accumulated in the lung, while PEGylated ONTs was mainly trapped in the liver and could circulate in the blood up to 24 hours. This study provided valuable information of physicochemical properties and the in vivo distribution behavior of PEGylated ONTs for their potential application into drug nanocarriers.

Molecular-Level Understanding of the Encapsulation and Dissolution of Poorly Water-Soluble Ibuprofen by Functionalized Organic Nanotubes Using Solid-State NMR Spectroscopy

A comprehensive study of the encapsulation and dissolution of the poorly water-soluble drug ibuprofen (IBU) using two types of organic nanotubes (ONT-1 and ONT-2) was conducted. ONT-1 and ONT-2 had similar inner and outer diameters, but these surfaces were functionalized with different groups. IBU was encapsulated by each ONT via solvent evaporation. The amount of IBU in the ONTs was 9.1 and 29.2 wt % for ONT-1 and ONT-2, respectively. Dissolution of IBU from ONT-1 was very rapid, while from ONT-2 it was slower after the initial burst release. One-dimensional (1D) (1)H, (13)C, and two-dimensional (2D) (1)H-(13)C solid-state NMR measurements using fast magic-angle spinning (MAS) at a rate of 40 kHz revealed the molecular state of the encapsulated IBU in each ONT. Extremely mobile IBU was observed inside the hollow nanosapce of both ONT-1 and ONT-2 using (13)C MAS NMR with a single pulse (SP) method. Interestingly, (13)C cross-polarization (CP) MAS NMR demonstrated that IBU also existed on the outer surface of both ONTs. The encapsulation ratios of IBU inside the hollow nanospaces versus on the outer surfaces were calculated by waveform separation to be approximately 1:1 for ONT-1 and 2:1 for ONT-2. Changes in (13)C chemical shifts showed the intermolecular interactions between the carboxyl group of IBU and the amino group on the ONT-2 inner surface. The cationic ONT-2 could form the stronger electrostatic interactions with IBU in the hollow nanosapce than anionic ONT-1. On the other hand, 2D (1)H-(13)C NMR indicated that the hydroxyl groups of the glucose unit on the outer surface of the ONTs interacted with the carboxyl group of IBU in both ONT-1 and ONT-2. The changes in peak shape and chemical shift of the ONT glucose group after IBU encapsulation were larger in ONT-2 than in ONT-1, indicating a stronger interaction between IBU and the outer surface of ONT-2. The smaller amount of IBU encapsulation and rapid IBU dissolution from ONT-1 could be due to the weak interactions both at the outer and inner surfaces. Meanwhile, the stronger interaction between IBU and the inner surface of ONT-2 could suppress IBU dissolution, although the IBU on the outer surface of ONT-2 was released soon after dispersal in water. This study demonstrates that the encapsulation amount and the dissolution rates of poorly water-soluble drugs, a class which makes up the majority of new drug candidates, can be controlled using the functional groups on the surfaces of ONTs by considering the host-guest interactions.

Preparation and formation process of Zn(II)-coordinated nanovesicles

Mixing a glycylglycine lipid and zinc acetate has been reported to form novel supramolecular Zn(II)-coordinated nanovesicles in ethanol. In this study, we investigate in detail the formation of nanovesicles by using three lipids at different temperatures and discuss their formation process. The original lipids show extremely low solubilities and appear as plate structures in ethanol. Within a small window of lipid solubility, the formation of lipid-Zn(II) complexes occurs mainly on the solid surfaces of plate structures. Controlling of the lipid solubility by temperature affects the kinetics of complex formation and the subsequent transformation of the complexes into nanovesicles and nanotubes. An improved method of two-step control of temperature is developed for preparing all the three kinds of nanovesicles. We provide new insights into the formation process of nanovesicles based on several control experiments. A tetrahedral lipid-cobalt(II) complex similarly produces nanovesicles, whereas an octahedral complex gives sheet structures. Mixing of zinc acetate with a β-alanyl-β-alanine lipid can only give sheet structures, which lack a polyglycine II hydrogen-bond network and induce no morphological changes. We conclude that the formation of the lipid-Zn(II) complexes on solid plate structures, tetrahedral geometry, and polyglycine II hydrogen-bond network in the complexes shall work cooperatively for the formation of Zn(II)-coordinated nanovesicles.

Soft Nanotubes Derivatized with Short PEG Chains for Thermally Controllable Extraction and Separation of Peptides

By means of a two-step self-assembly process involving three components, including short poly(ethylene glycol) (PEG) chains, we produced two different types of molecular monolayer nanotubes: nanotubes densely functionalized with PEG chains on the outer surface and nanotubes densely functionalized with PEG chains in the nanochannel. Turbidity measurements and fluorescence spectroscopy with an environmentally responsive probe suggested that the PEG chains underwent dehydration when the nanotubes were heated above 44–57 °C and rehydration when they were cooled back to 25 °C. Dehydration of the exterior or interior PEG chains rendered them hydrophobic and thus able to effectively extract hydrophobic amino acids from the bulk solution. Rehydration of the PEG chains restored their hydrophilicity, thus allowing the extracted amino acids to be squeezed out into the bulk solutions. The nanotubes with exterior PEG chains exhibited selectivity for all of the hydrophobic amino acids, whereas the interior PEG chains were selective for hydrophobic amino acids with an aliphatic side chain over hydrophobic amino acids with an aromatic side chain. The higher selectivity of the latter system is attributable that the extraction and back-extraction processes involve encapsulation and transportation of the amino acids in the nanotube channel. As the result, the latter system was useful for separation of peptides that differed by only a single amino acid, whereas the former system showed no such separation ability.