Stability and release of bioactives from liposomes

The health benefits of bioactive compounds have been proved beyond doubt, but their instabilities and poor bioavailabilities most often limit their full potential. Encapsulating them in vesicular carrier systems, such as liposomes or emulsions, protects the sensitive compounds against damaging factors and offers an opportunity to achieve controlled release, which in turn aims to enhance their bioavailabilities and efficacies. Liposomes and emulsions are regularly used to tackle the stability issues of bioactives, however, they themselves are susceptible to various chemical, physical, and biological instabilities. Different factors related to lipids, bioactives, and liposome size and lamellarity are known to affect both the stabilities and release behavior of liposomes. Liposomes show biphasic or triphasic release patterns with an initial burst release which is brought under control to achieve better release properties. Optimizing release-affecting factors, utilization of the bioactive–cyclodextrin complex, polymeric coating of liposomes, or encapsulation of liposomes into another polymeric matrix are reported to control the liposomal release behavior. Moreover, liposomes are designed to hold (slow or no release) their content until stimulated/triggered by some release-triggering mechanism like pH, temperature, ultrasound, etc. In comparison, double/multiple emulsion and polyelectrolyte coated multilayer emulsions can also offer controlled release of their payload. Liposomes, being made of natural ingredients, are an attractive choice as carriers for bioactives, although some challenges remain. The first is the destruction of liposomes by bile and lipases in the gastrointestinal tract, the most plausible route of administration for bioactives. In addition, they do not permeate through the gastrointestinal epithelial layers. A large amount (often 20%–30%) of cholesterol, a common ingredient required for liposome rigidity, also remains a concern for hypercholesterolemic people. However, our intense interest in bioactive substances can be expected to overcome these challenges in the near future.