International Journal of Molecular Sciences
1. Introduction
During the past few decades, there has been a tremendous growth in the use of biologics for regenerative medicine applications [1,2].
Biologics currently available for clinical use include platelet rich plasma, bone marrow aspirate, lipoaspirate, amniotic allograft suspension, umbilical cord-derived Wharton’s Jelly, cord blood, and exosomes [3,4]. The e cacy of these biologics is attributed to the presence of stem cells, growth factors (GFs), cytokines (CKs), and extracellular vesicles (EVs), including exosomes [5,6].
The use of stem cells, including mesenchymal stem cells (MSCs), for clinical application in regenerative medicine, has gained substantial interest. MSCs can be obtained from several sources, including bone marrow, adipose tissue, trabecular bone, and deciduous teeth [7–10]. MSCs likely exert their therapeutic effect by migration to the sites of injury, engrafting, and interacting with other cells after administration [11]. Despite their therapeutic benefits, MSCs present several disadvantages, including establishing a reliable source with stable phenotype, genetic instability and chromosomal aberrations, intravenous administration-related toxicity caused by physical trapping of the cells in the lung microvasculature, rejection by the host, formation of ectopic tissue, and tumorigenicity [11–13].
The beneficial effects of MSCs may well not result from their ability to differentiate, but from their secretion of bioactive molecules such as GFs, CKs, and exosomes [14–16]. GFs are a heterogenous group of peptides/proteins and lipid soluble factors secreted by various cells including MSCs. GF receptor activation induces signal transduction pathways which initiate cell migration, proliferation, growth, and differentiation [17]. CKs are low molecular weight proteins responsible for regulation of inflammation, immune response, cellular differentiation, and tissue remodeling [18]. GFs and CKs frequently have overlapping and synergistic actions with immense potential in regenerative medicine [19]. These factors can act in an autocrine or paracrine manner: a single cytokine can promote the synthesis and release of additional CKs, leading to a cascade of molecules, influencing cell division, differentiation, and regeneration of various tissues and organs [6].
Exosomes are secreted by MSCs and act as paracrine mediators between MSCs and target cells, providing a regenerative microenvironment for damaged tissues [16,20,21]. Exosomes are small EVs with a diameter from 30–150 nm. They are formed from a sequential process of multivesicular body membrane remodeling. Exosomes are present in body fluids, including blood plasma, amniotic fluid, and umbilical cord-derived Wharton’s jelly [22]. MSCs-derived exosomes can recapitulate the MSC’s biological activity and can act as a cell-free therapeutic alternative to whole cell therapy with great regenerative potential [23–25]. The use of exosomes can o er advantages over whole cell therapy given their higher safety profile, lower immunogenicity, and inability to directly form tumors [26]. In addition, given their smaller size, exosomes can potentially migrate to target organs e ciently after injection, without getting trapped in the lung microvasculature [26,27].
Considering the benefits of cell-free GFs, CKs, and exosomes, and the disadvantages of whole cell therapy, innovative and effective cell-free products should be considered for clinical applications. We have formulated a novel cell-free, stem cell-derived extract (CCM) and characterized it for the presence of GFs, CKs, and EVs, including exosomes. We hypothesized that numerous GFs, CKs, and EVs, including exosomes, would be present in this formulation. This preliminary study describes the preparation and characteristics of this novel cell-free stem cell-derived extract.