However, the efficacy of nutraceuticals is a function of absorption and bioavailability after ingestion. Absorption refers to the process of a molecule’s movement from ingestion to its entry into systemic circulation. Bioavailability refers to the amount of the molecule that was absorbed and reached systemic circulation relative to what was ingested.
As consumers and brands begin to recognise the importance of bioavailability, a working knowledge of the mechanisms and interactions that affect nutraceutical bioavailability is imperative for determining the best approach for development of novel and innovative advanced delivery systems.
Novel Advanced Delivery SystemsNutraceutical ingredients such as quercetin, curcumin, resveratrol, and vitamin D3all have demonstrable beneficial effects on health but, due to their lipophilicity, they are poorly soluble in the aqueous environment of the gastrointestinal tract. Therefore, an effective delivery system is required to enhance their absorption and subsequent efficacy.
There is no-one-size-fits-all solution, and the right delivery system must be carefully selected based on various factors including the active ingredient, the final dosage format (i.e., tablet, capsule, powder, liquid spray, effervescent, etc), and the end user.
Here come liposomesLiposomes are tiny, spherical, engineered, nanostructures that are mainly made up of a lipid bi-layer membrane around an aqueous core. They are mainly made up of biological materials, so they are seen by the body as inert. Both hydrophilic and lipophilic active ingredients can be incorporated into the liposome to achieve targeted delivery of your desired active to the cells that need it.
Liposomes rely on electrostatic charge, between the lipid molecules, to keep the membrane in place. They also rely on the subsequent electric potential at the interface of the lipid bi-layer and the liquid carrier (in our case, water).
As liposomes are generally below the visible wavelength of light (380 to 700 nm2) it is not possible to see them using a standard light microscope. So, how do you confirm that you have actually made liposomes and not a "soup" of ingredients?
Other than particle size and distribution, two important tools around the characterisation and presence of liposomes are zeta potential and transmission electron microscopy imaging.
Zeta potentialZeta potential is the electric potential at the interface of the lipid bi-layer and the water surrounding it.
Colloidal dispersions (eg, liposomes in water) with a medium to high zeta potential (negative or positive charge greater than 20 eV) are electrically stable while those with a low zeta potential (anything below 20 eV) are unstable and tend to coagulate or flocculate (clump).
Also, zeta potential is one of the available tools to characterise a double layer, such as that in a liposome. The below chart shows the difference between a particular formulation made by two different manufacturers using different methods of manufacture.
Pharmako Biotechnologies Competitor Liposomal D3
Competitor Liposomal D3
PlexoZome® D3 – high zeta – low zeta potential means
Potential means more less stability and high coagulation. stability and no coagulation.
TEM (Transmission Electron Microscopy) imagingTEM is an imaging technique that uses an electron beam to image a nanoparticle sample. It provides much higher resolution than is possible with light-based imaging techniques.
TEM is an important method for the characterisation of the presence, size and shape of liposomes. It can directly visualise single particles (at the low end nano scale) and even go into detail of their inner structure, eg lipid bi-layer. There are two distinct methods for TEM visualisation. One is cryo-electron microscopy (cryo-TEM) and the other is negative staining TEM.
Liposomes need to be preserved for the electron microscope to best visualize them close to their native structure. As such, cryo-TEM is best suited for this application. Cryo-TEM uses thin films of suspensions that are plunge frozen to create vitrified ice films that can be imaged directly in the electron microscope under liquid nitrogen temperature. This requires very expensive equipment, detailed methods, and experienced operators, hence it is not commercially readily available.
The other method is negative staining TEM (usually with uranyl acetate). As liposomes do not have enough contrast they need to be stained in order to distinguish their features. Negative staining TEM is faster and simpler than cryo-TEM. It also requires less advanced equipment, methods and is more readily available.