Indeed, researchers are beginning to recognize the advantages exosomes hold over other drug carrier systems. Owing to these properties, exosomes have the potential to overcome several of the limitations associated with other drug delivery systems. Finally, exosomes have an excellent tissue/cell penetration capacity. Due to their endogenous origins, exosomes also exhibit high biocompatibility. Their lipid bilayer also minimizes immunogenicity and toxicity, supporting their stabilization into the extracellular space. Firstly, they are innately stable due to their lipid bilayer membrane, allowing them to circulate even in the harsh tumor microenvironment. To understand how these small particles can induce such large-scale effects, let’s consider their unique properties. Though exosomes are involved in important physiological activities, they also play a significant role in the pathogenesis of diseases including cancer, cardiovascular and neurodegenerative diseases, and viral infections. Exosomes are effective cellular transport systems, capable of shuttling bioactive ‘cargo’ such as proteins, lipids, and nucleic acids. Exosomes permit efficient intercellular communication and signaling between cells and across biological barriers (including the blood-brain barrier). The exosomal pathway of intercellular traffic plays a significant role in many features of health and disease, including immunity, tissue homeostasis, and regeneration. Exosomes are also present in a variety of biological fluids such as blood, urine, saliva, breast milk, amniotic, synovial, cerebrospinal fluids, and even tears. Since their initial characterization, further studies have revealed that exosomes are secreted by most viable cell types, including immune cells, intestinal epithelial cells, and neurons. The inset shows the molecular constituents of the exosomes. Schematic representation of exosome biogenesis and secretion. Upon release from the secreting cell, they transmit messages to recipient cells through several mechanisms, including surface receptor interaction, membrane fusion, as well as receptor-mediated endocytosis, phagocytosis, and/or micropinocytosis (Figure 1).įigure 1. Produced in the endosomal compartment of most eukaryotic cells, exosomes are subsequently released into the extracellular space by fusion with the plasma membrane. However, exosomes were found to be more complex in structure, containing a large array of proteins and lipids. Like liposomes, exosomes are comprised of a lipid membrane and an inner aqueous medium. Yet it was not until the 1980s that these 30–150nm extracellular vesicles were first defined and the name ‘exosomes’ was coined. They found that this material - which they termed “platelet dust” - was lipid-rich and likely to be involved in platelet activation. It was over 50 years ago that researchers first observed minute particulates in human plasma. Using insights from the CAS Content Collection™, we provide a landscape view of recent research advancement on exosome applications, while highlighting the opportunities and challenges in this rapidly expanding area. In this three-part series, we explore the history of exosomes, before describing the latest exosomal research in drug delivery and diagnostics. To predict and fully leverage the potential of the exosome, it is important to understand the depth and breadth of the research landscape. Their promise in therapeutics and diagnostics is garnering interest from both corporate and academic institutions. They are gaining the attention of the scientific community due to their ability to carry messages between cells in the form of proteins, nucleic acids, and other biomolecules. Dubbed ‘nature’s lipid nanoparticles’, exosomes are a subset of extracellular vesicles released from cells as part of their normal physiology or under certain pathologies.
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