Plants extracts loaded in nanocarriers: An emergent formulating approach

Over the millennia, plants have represented for Humankind the main source of food, but also a vast resource to maintain health, for prophylactic properties or to cure human and animal diseases. Presently, between 65 and 80% of populations in developing countries use medicinal plants as therapeutic remedies for their primary healthcare and in Europe and USA there is an increasing demand of botanical products both on the form of food supplements and herbal medicinal products. Botanicals on the market are mainly based on traditional (infusions or decoctions), conventional (using organic solvents) and innovative (supercritical CO2 or subcritical water) extracts but there is an increasing demand of essential oils for aromatherapy. Conversely, the clinical use of many extracts is limited due to the need of repeated administrations or high doses because of low hydrophilicity and intrinsic dissolution rate(s), or physical/ chemical instability. Other limits are low absorption, poor pharmacokinetics and bioavailability, scarce biodistribution, first pass metabolism, trivial penetration and accumulation in the organs of the body. In the case of essential oils, the high volatility and instability are further limitations. Nowadays, the design and production of appropriate drug delivery systems, in particular nanosized ones (between 50 and 300 nm), have already entered into clinical use and can offer an advanced approach to optimized the therapeutic efficacy of extracts and essential oils. A successful drug carrier system should have optimal drug loading and release properties, a long shelf life, and exert a much higher therapeutic efficacy as well as lower side effects. Polymeric nanoparticles and lipid based-nanocarriers including micelles, vesicles, nanocochleates, micro- and nanoemulsions represent successful examples of extract nanoformulations overcoming these limitations. This review reports on some paradigmatic success stories of extract and EO nanoformulations with remarkable advantages over conventional formulations, which include increase of solubility, stability, permeation and bioavailability, sustained delivery. Paradigmatic examples include formulations of extracts from Vitex agnus-castus, Sylibum marianum, Phyllanthus amarus, Ginkgo biloba, Panax notoginseng, Hypericum perforatum and thyme essential oil.