What is a Liposome?

(lĭp′ə-sōm′, lī′pə-)

Not discernable with a light microscope, a nanoliposome can be seen under an electron microscope as a sphere. Just as a water balloon has a thin outer layer with a water-filled interior, a liposome likewise has a thin outer wall — similar to a membrane — made of a phospholipid bilayer and an interior containing a water-soluble material. First identified in the early 1960’s, liposomes have undergone extensive research, the aim being the optimization of encapsulation, stability, circulation time and targeted delivery of its cargo, which may be a drug or a nutrient to a specific site of action. Until recently, the use of liposomes as a carrier of nutriments was limited, the delivery of drugs being more the focus. Their versatility is now being realized in other domains.

A few companies are pioneering the benefits of this unique science. It has long been the case that absorption and bioavailability rates of oral dietary and nutritional tablets and capsules is low and unreliable. Now, the natural encapsulation of lipophilic and hydrophilic nutrients within a liposome has created an effective method of bypassing the destructive elements of the digestive system, allowing the encapsulated nutrient to be delivered directly to cells and tissues.

To make a suitable microscope image, the liposomes are frozen and then sliced into ridiculously thin layers. This “freeze fracturing” will open some, but not all, and you will be able to distinguish the intact spheres from the concave surfaces of the incised liposomes. If this arrangement fails to emerge, you most likely do not have liposomes. But most clinics and manufacturers do not own electron microscopes. So, how do you determine that you have liposomes? Mix your material with water. Solid globs of amorphous matter are not carrying anything inside them and are not liposomes. If this happens, the phosphatidylcholine (PC) content is either too low, of poor quality, or is non-existent. If what you think is a liposome appears to be floating in foam, you are stuck with a mere emulsion, not a liposome. The liquid around a liposome should be clear.

Liposomes do not form spontaneously, typically needing energy applied to a dispersion of PC in a polar solvent, such as water. Heat, agitation and the aqueous province of the human body afford the right conditions. Sonication of phospholipids in water does the same thing, but likely will form layers like those of an onion, with progressively smaller liposomes. The inclusion of ancillary lipids facilitates the preparation. Microscopic vesicles — nanoliposomes — of PC can trap desirable payloads and provide controlled release of various bioactive agents at the right place at the right time. Here, otherwise volatile, reactive or sensitive additives become stabilized. Liposomes are bioresponsive because they and cell membranes share a common constituent — the lipid bilayer. As liposomes and cell membranes sidle near each other, they become conjugated and meld into each other, allowing the liposomal cargo to be deposited in the cellular cytosol, where its ameliorative destiny can be fulfilled. Liposomes with target specificity offer the prospect of safe and effective therapy for challenging clinical uses.

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