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Direct visualization of dispersed lipid bicontinuous cubic phases by cryo-electron tomography.

Demurtas D, Guichard P, Martiel I, Mezzenga R, Hébert C, Sagalowicz L - Nat Commun (2015)

Bottom Line: Moreover, their biocompatibility is attractive for nutrient or drug delivery system applications.Here the three-dimensional organization of dispersed cubic lipid self-assembled phases is fully revealed by cryo-electron tomography and compared with simulated structures.Therefore, compositional gradients within cubosomes are inferred, with a lipid bilayer separating at least one water channel set from the external aqueous phase.

View Article: PubMed Central - PubMed

Affiliation: Interdisciplinary Centre for Electron Microscopy, Swiss Federal Institute of Technology (EPFL), Lausanne 1015, Switzerland.

ABSTRACT
Bulk and dispersed cubic liquid crystalline phases (cubosomes), present in the body and in living cell membranes, are believed to play an essential role in biological phenomena. Moreover, their biocompatibility is attractive for nutrient or drug delivery system applications. Here the three-dimensional organization of dispersed cubic lipid self-assembled phases is fully revealed by cryo-electron tomography and compared with simulated structures. It is demonstrated that the interior is constituted of a perfect bicontinuous cubic phase, while the outside shows interlamellar attachments, which represent a transition state between the liquid crystalline interior phase and the outside vesicular structure. Therefore, compositional gradients within cubosomes are inferred, with a lipid bilayer separating at least one water channel set from the external aqueous phase. This is crucial to understand and enhance controlled release of target molecules and calls for a revision of postulated transport mechanisms from cubosomes to the aqueous phase.

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Related in: MedlinePlus

3D organization of the liquid crystal region inside a cubosome.(a) Sequence of images extracted from the tomogram along the z direction. It shows both the first (red box) and second (blue box) network in alternate position indicating the sequence of the channels (we adopted arbitrarily the term of ‘first and second' to differentiate the two interdependent networks). (b) Central core of the original tomogram used for the subtomogram averaging process and its 3D reconstruction showing the unit cells. (c) Extract of the tomogram showing one of the two water channel network. Red arrows show the nodes and the enlargement of the water network. (d–e) Top and side view of the filtered 3D reconstruction where the pores belonging to the first (red arrows) and second network (blue arrows) are indicated (rendering of the subtomogram averaging in Supplementary Movie 1).
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f2: 3D organization of the liquid crystal region inside a cubosome.(a) Sequence of images extracted from the tomogram along the z direction. It shows both the first (red box) and second (blue box) network in alternate position indicating the sequence of the channels (we adopted arbitrarily the term of ‘first and second' to differentiate the two interdependent networks). (b) Central core of the original tomogram used for the subtomogram averaging process and its 3D reconstruction showing the unit cells. (c) Extract of the tomogram showing one of the two water channel network. Red arrows show the nodes and the enlargement of the water network. (d–e) Top and side view of the filtered 3D reconstruction where the pores belonging to the first (red arrows) and second network (blue arrows) are indicated (rendering of the subtomogram averaging in Supplementary Movie 1).

Mentions: Cubosomes in a size range of 100–300 nm were chosen for 3D reconstruction, since their low thickness leads to a high signal-to-noise ratio. The sequences of images extracted from the tomogram in the z direction show holes belonging to the water channels (Fig. 2a). When progressing along the z direction, the periodic network is shifted by half of the diagonal of the cube (a√3/2, where a is the lattice parameter). This provides a direct and separate visualization of the two independent networks indicated by the red and blue box (first and second network).


Direct visualization of dispersed lipid bicontinuous cubic phases by cryo-electron tomography.

Demurtas D, Guichard P, Martiel I, Mezzenga R, Hébert C, Sagalowicz L - Nat Commun (2015)

3D organization of the liquid crystal region inside a cubosome.(a) Sequence of images extracted from the tomogram along the z direction. It shows both the first (red box) and second (blue box) network in alternate position indicating the sequence of the channels (we adopted arbitrarily the term of ‘first and second' to differentiate the two interdependent networks). (b) Central core of the original tomogram used for the subtomogram averaging process and its 3D reconstruction showing the unit cells. (c) Extract of the tomogram showing one of the two water channel network. Red arrows show the nodes and the enlargement of the water network. (d–e) Top and side view of the filtered 3D reconstruction where the pores belonging to the first (red arrows) and second network (blue arrows) are indicated (rendering of the subtomogram averaging in Supplementary Movie 1).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4660369&req=5

f2: 3D organization of the liquid crystal region inside a cubosome.(a) Sequence of images extracted from the tomogram along the z direction. It shows both the first (red box) and second (blue box) network in alternate position indicating the sequence of the channels (we adopted arbitrarily the term of ‘first and second' to differentiate the two interdependent networks). (b) Central core of the original tomogram used for the subtomogram averaging process and its 3D reconstruction showing the unit cells. (c) Extract of the tomogram showing one of the two water channel network. Red arrows show the nodes and the enlargement of the water network. (d–e) Top and side view of the filtered 3D reconstruction where the pores belonging to the first (red arrows) and second network (blue arrows) are indicated (rendering of the subtomogram averaging in Supplementary Movie 1).
Mentions: Cubosomes in a size range of 100–300 nm were chosen for 3D reconstruction, since their low thickness leads to a high signal-to-noise ratio. The sequences of images extracted from the tomogram in the z direction show holes belonging to the water channels (Fig. 2a). When progressing along the z direction, the periodic network is shifted by half of the diagonal of the cube (a√3/2, where a is the lattice parameter). This provides a direct and separate visualization of the two independent networks indicated by the red and blue box (first and second network).

Bottom Line: Moreover, their biocompatibility is attractive for nutrient or drug delivery system applications.Here the three-dimensional organization of dispersed cubic lipid self-assembled phases is fully revealed by cryo-electron tomography and compared with simulated structures.Therefore, compositional gradients within cubosomes are inferred, with a lipid bilayer separating at least one water channel set from the external aqueous phase.

View Article: PubMed Central - PubMed

Affiliation: Interdisciplinary Centre for Electron Microscopy, Swiss Federal Institute of Technology (EPFL), Lausanne 1015, Switzerland.

ABSTRACT
Bulk and dispersed cubic liquid crystalline phases (cubosomes), present in the body and in living cell membranes, are believed to play an essential role in biological phenomena. Moreover, their biocompatibility is attractive for nutrient or drug delivery system applications. Here the three-dimensional organization of dispersed cubic lipid self-assembled phases is fully revealed by cryo-electron tomography and compared with simulated structures. It is demonstrated that the interior is constituted of a perfect bicontinuous cubic phase, while the outside shows interlamellar attachments, which represent a transition state between the liquid crystalline interior phase and the outside vesicular structure. Therefore, compositional gradients within cubosomes are inferred, with a lipid bilayer separating at least one water channel set from the external aqueous phase. This is crucial to understand and enhance controlled release of target molecules and calls for a revision of postulated transport mechanisms from cubosomes to the aqueous phase.

Show MeSH
Related in: MedlinePlus