Absorption of dietary substances or supplements (“actives”) requires, first, transfer from the originally provided form to the cells of the GI tract. If the active is a solid, then generally as an intermediate step it must transfer through a liquid on the way to these cells. Since the GI tract is principally an aqueous environment, it’s best for the active to be able to transfer through water.
But this doesn’t complete the process: the active must effectively make its way from these GI tract cells to the target cells within the body – which might be muscle cells, for example. There are several different mechanisms of absorption from the GI tract, and different mechanisms will give different bioavailabilities for different substances.
So generally speaking, you want to find a delivery method that efficiently transfers a substance (which might ordinarily be solid; for example, a powder) through the aqueous environment to the cells of the GI tract; and then secondly, this method should have a particular mechanism of absorption that gives high bioavailability.
A number of valuable compounds have terrible water solubility and don’t transfer well through water. And, further, they tend to have poor bioavailability even when absorbed – for example, being largely destroyed by first-pass metabolism.
Microemulsions were developed by the pharmaceutical industry to give excellent results in exactly such situations. They work by dispersing actives into extremely small, nano-meter scale micelles by using an excipient mixture comprised of a surfactant, a cosurfactant, and, optionally, a lipid as excipients. It’s required that these components have differing and usually very exact hydrophilic/lipophilic balances. These requirements will vary according to the actives being delivered.
If the mixture is exactly correct in the GI tract, the formulation generates micelles so small as to give a transparent solution in water. They provide extremely efficient transfer of the active to the cells of the GI tract. This is largely a result of the vast increase in effective solubility.
Another advantage is that in many cases bioavailability is yet further enhanced, due both to greatly improved mass transfer and, in those cases where this method works especially well, higher efficiency of delivery to the cells of the body as well, due to change in absorption mechanism.
Biotest’s first such formulation was for the capsule form of MAG-10, which incidentally was a really remarkable challenge as the amounts of actives, and their physicochemical properties, were well beyond anything done before. It took a very precise and exact mixture to achieve this. Including any of the most commonly used excipients for this purpose, even in trace amounts, incidentally, resulted in failed tests: MAG-10 worked only within a very narrow window of ratios of some rather exotic things. So it was a specific technology, which we referred to as nano-dispersion technology as that is exactly what it does.
There’s no “one size fits all” answer to developing such formulations, however.
Formulations we have now done for different actives have required different surfactants, co-surfactants, and/or lipids – or they’ve required them in different ratios, which incidentally is why they appear different. It’s actually quite interesting research, as it’s both art and science. While science can guide you in making good choices of things to try, it’s an art to find the exact mixtures that test as giving the best results.
There are also times, incidentally, when no advantage is found! So nano-dispersion technology is not something that has to be used for everything. But for some things, it is of great value.
