Liposomes are hollow vesicles of nano-metric size with an outer membrane composed of phospholipids. They can be used as agents for the supply of drugs and genes; in fact, its use has been authorized to carry out different clinical trials. [1]
The advantage of liposomes is that they are internalized well by the cell. During this process, the cell isolates them from the rest of the cell with the endosome, a kind of safety carrier that carries the different substances it takes from the external environment from the cell membrane to the lysosomes, where they are “digested.” Controlled release from lysosomes as a “product of digestion” can significantly increase the supply of drugs directly into target cells.
The key to finding liposomes that are able to release their drug load optimally when they reach the lysosomes lies in the nature of the chemical bonds. Since the inside of the lysosomes is acidic, the ideal is that the liposomes are pH-sensitive. The problem is that most of the phospholipids that are used to prepare liposomes have covalent (stable) bonds, so they do not react quickly enough to the acidic environment, which limits the release of the charge, in addition to needing synthesis processes in the laboratory they are long and complex.
Uses and applications
Although initially the liposomes developed as a membrane model and were used to conduct studies and experiences related to it, its characteristics, composition, behavior against certain agents such as surfactants, membrane proteins, etc., were soon intuited. and developed other applications thereof, mainly as vectors or vehicles of pharmaceutical, cosmetic or dietary active ingredients, in addition to some other industrial or technical applications of various types.
To facilitate the explanation and presentation of the different applications of liposomes, these can basically be divided into medical or biological applications and non-medical or non-biological or technical applications.
Medical or biological applications
Liposomes are used, mainly, to transport active ingredients or medications in the most selective way possible, increasing their effeciveness and reducing their unwanted effects, especially their toxicity.
Its size and physicochemical characteristics make these vesicles or structures circulate, penetrate and diffuse into the Issues with great ease, releasing the active ingredient in them encapsulated in a controlled and more effecive way.
This change in the pharmacokinetics of the active substance will have a significant impact on the pharmacodynamic characteristics of the same, which, almost always, results in a general improvement in the activity of the product and a decrease in its toxicity or unwanted effects. (See: Liposomes with active substance).
The structure and physicochemical characteristics of liposomes allow incorporating active ingredients separately or together, both water-soluble and fat-soluble. The fat-soluble active ingredients are incorporated in the lipid phase, while the water-soluble ones are incorporated, mainly, in the internal aqueous phase of the liposome and also in the external aqueous phase.
The part of active ingredient dissolved in the external aqueous phase of the liposome, if necessary, can be eliminated by different filtration or separation techniques, although this is not always easy or possible. [2]
Liposomes are often used to prolong the action, improve absorption, change the route of administration or simply to solubilize or stabilize a certain active ingredient or a set of them. (See: General stability of liposomes).
Generally, the bioavailability of substances encapsulated in liposomes is greatly increased, increasing the effectiveness, intensity, and duration of their effects. (See; Reactor effect, orderly transfer, potential difference, … of the liposomes).
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