Introduction
Extracellular vesicles (EVs) including exosomes, microvesicles, and
apoptotic vesicles, are membrane-bound small structures released from
cells into the surrounding environment (1). They play essential roles in
intercellular communication, particularly exosomes, which contain
several constituents from the cells that secrete them, and appear to be
involved in the pathogenesis of various disorders, including cancer,
neurodegeneration, and inflammatory diseases (2). Interestingly, the
biocompatibility of exosome, their circulating stability, and
bioavailability in vivo, allowed them to gain increasing attention as an
emerging drug delivery methodology over the last decade (3). They
represent an important pathway to transfer information between cells,
and thus, might be developed to package and deliver therapeutic
molecules. Although exosomes are not nanoparticles derived from the
nanotechnology due to its non-mankind nature, they may act as a
Nano-carrier owing to their particle diameter (4), which is estimate to
be between 30-100nm, and thus, can be used to load a variety of small
bioactive molecules to improve bioavailability. Therefore, exosome’s
particle size allows them penetrate deep into the tissues and overcome
barriers such as the blood-brain barrier and the deformable
cytoskeleton. Another important character is that they have a slightly
negative zeta potential, which guarantees their long circulation (5). In
addition, some exosomes are capable of escaping from the immune system
and have shown to have a low immunogenicity, and high stability in the
blood, which prolongs drug circulation within the body (6).
Generally, exosomes are excreted from different types of cells and found
abundantly in animal milk, which confirmed to contain relatively a
stable structure and were shown to contain different miRNAs, including
miRNA-148a-3p (7). Since bovine milk exosomes are protected from
degradation by stomach acids (2, 8), milk exosomes are, therefore,
considered to be useful for drug-delivery systems (DDSs), hence, milk
exosome-encapsulated formulations can be used for therapeutic purposes
(9). Therefore, milk-derived exosomes are seeing as promising new drug
carriers for reaching distant tissues (10, 11).
Mare’s milk is the national drink of the indigenous population in
Central Asia, including Kazakhstan. Recent scientific data on the
characteristics of the composition of horse milk and their potential
properties that contribute to improving health have increased interest
in this dietary source (12). Mare’s milk shares some similarities to
human breast milk and therefore, may have some valuable therapeutic
properties (13). Mare’s milk has a very good hygienic and sanitary
status, differs from the milk of other farm animals in that it has the
lowest somatic cell content and a very low total number of
microorganisms (14). There are no studies examine the use of mare’s
milk-derived exosomes as a form of therapeutic carriers. Therefore, the
current study aims to extract mare’s milk-derived EVs, and isolate high
content exosomes to test their suitability as a reliable form of
therapeutic drug carrier. However, milk-derived EVs significantly
different in size ranging from 30nm-10µm, and possibly contain various
constituents, thus we do not exactly know which EVs extraction methods
would allow us to have the optimum exosomal size. Thus, there is a need
to compare and characterize different methods that allows isolation of
the highest concentration of exosomes with the most homogenous shapes
and sizes.