Technical Summary- An Inrtoduction to Lipid Nanoparticals
The most common type of lipid nanoparticle, a liposome, can be thought of as a hollow sphere whose size ranges from 30 nanometers to 10,000 nanometers or 10 microns. A nanometer, usually abbreviated as nm, is 1 millionth of a millimeter.
For comparison, a red blood cell is about 8,000 nanometers and viruses range from 25 – 200 nanometers. Liposomes are made from phospholipid molecules which are the same molecules that comprise cell membranes. Phospholipids are amphipathic, that is, part of their structure is water-soluble (hydrophilic or water-loving) and the other part is oil-like (hydrophobic or water-fearing or fat-soluble). Therefore, when added to water, the water-soluble part of the phospholipid interacts with the water and the oil-like part of the molecule avoids the water.
In order to accomplish this, the phospholipids align themselves side-by-side with their oil-like portions orienting themselves towards each other. This structure is known as a phospholipid bilayer. This bilayer extends itself in water to form a sheet which then curls into a liposome. Liposomes smaller than about 200 nm usually only consist of one bilayer (unilamellar liposomes) but larger liposomes can contain concentric layers of lipid (like an onion) or several smaller liposomes can be formed inside large liposomes. These larger multicompartmented liposomes are known as multilamellar liposomes.
The interior of liposomes is filled with water and therefore, molecules which are soluble in water can be encapsulated in the interior of the liposome. A less recognized but very important property of liposomes is that molecules which are not water soluble, or oil-like, can be entrapped in the oil-like portion of the phospholipid bilayer. Consequently, liposomes can serve as carriers for all types of molecules including both water-soluble and water-insoluble compounds. In fact, a single liposome can carry both types of molecules or combinations of each type of molecule.
Liposomes can be made of a single type of phospholipid or by mixtures of different phospholipids. Non-phospholipid components such as cholesterol, fatty acids and other lipid soluble molecules such as vitamin E, vitamin A and coenzyme Q10 are commonly added to liposomal membranes. By varying the type of phospholipid used to make liposomes and/or by attaching certain molecules to the surface of liposomes, they can be engineered to have many useful properties.
Liposomes can be designed to:
Mask the taste of nutrients such as amino acids which have a very bitter taste.
Evenly distribute fat-soluble (oil-like) compounds such as certain vitamins, antioxidants, antibiotics, flavors, etc. which often can’t be mixed in water-based products including most foods.
Protect compounds such as vitamins and antioxidants from premature oxidation for increased shelf-life.
Release their contents when they reach a specific temperature.
Release their contents at a specific pH value.
Target certain tissues or cell types by changing the types of lipids in the liposome.
Target tissues, cell types or specific proteins by attaching antibodies to the surface.
Fuse with cells, which is important in delivering DNA to a cell.
Serve as model cell membranes making it easier to study specific cellular processes and how certain molecules, such as drugs, interact with cells.
Protect compounds from acidic and enzymatic degradation in the stomach and intestine by using certain lipids to make the liposome and/or molecules to coat the liposome.
Enhance the intestinal absorption of compounds by coating with certain molecules.
Carry drugs across the nasal mucosa (nasal drug delivery).
Deliver drugs directly to lung tissue by inhalation of the liposomes.
These are only a few of the applications for which liposomes have been used. Reports of new types of liposomes and as well as new uses for liposomes seem to appear almost daily.
Please note that liposomes have to be specially engineered to perform most of the functions listed above. For example, liposomes need to be coated with specific molecules in order to deliver compounds across the intestines. While this research is in its early stages, it promises to accomplish a feat once thought impossible for liposomes. Especially important when considering this research is that although orally dosed liposomes have been shown to deliver intact, active protein molecules such as insulin into the bloodstream (proteins like insulin are normally broken apart into their component amino acids in the harsh, acidic environment of the stomach), the liposomes themselves have not been shown to enter the bloodstream after oral dosing. So while intravenously dosed liposomes of certain types can target particular organs, such as the liver, and even tumors, this is only true for liposomes that are injected directly into the bloodstream. Since orally dosed liposomes do not appear to enter the bloodstream, these liposomes do not have the same targeting properties as intravenously dosed liposomes. Some liposome vendors fail to recognize this important difference between orally and intravenously dosed liposomes.
Other liposome vendors make unreasonable promises such as delivering nearly 100% of the liposomal compound orally or through the skin. Yet they show no data to support such fantastic results. Without having done the experiments how do they know that this high delivery rate is occurring?
There are products labeled as liposomes sold that are not liposomes at all. The product contains the components of liposomes plus compounds that are supposed to be encapsulated however there is either not enough water for the liposomes to form, or solvents such as ethanol (ethyl alcohol) which prevents liposomes from forming, or both. These products are intended to form liposomes when added to water-based drinks. We find that these products do not disperse in water and tend to form large “clumps” of lipid in the bottom of the glass and cannot be evenly dispersed in water even with several minutes of vigorous stirring. True liposomes are very small, fine particles much too small to be seen by eye. Even when the liposomes settle in water as they sometimes do it should be very easy to resuspend them with a quick stir or shake. Higher concentrations of liposomes appear very smooth and creamy and will either result in an almost clear or slightly cloudy suspension when dispersed in water. Either way, no large “clumps” should be present.
The scientists at NanoLife Nutra thoroughly understand not only the behavior of lipids and liposomes, but also the scientific process that must be used to design liposomes for various purposes. We will always provide full disclosure as to the nature of the liposomes and their contents in the product and purpose for which those liposomes were designed.
Copyright by Encapsula NanoSciences 2014
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