About Extracellular Vesicles
Extracellular vesicles, including microvesicles, microparticles and exosomes (1) are abundantly present within the plasma and hitherto were considered as the “garbage bags” of the cells released in the plasma for removal. This view has changed dramatically in the last few years.
Extracellular vesicles are secreted by all cells especially after stimulation. These vesicles are important in cell-to-cell communication in a variety of processes (Figure 1) including coagulation (2), antigen presentation (3) and tissue damage (4). Plasma extracellular vesicles can be easily isolated from frozen plasma or serum and contain protein, miRNA and RNA depending on source and stimulus involved. Isolating these vesicles from the blood and study their content provides information on the pathological status of cells and the physiological and pathophysiological processes they are involved in, without the confounding background of the highly abundant plasma proteins and for this form a source of biomarkers for diagnosis and prognosis of disease (5,6).
Diagnosis and prognosis
Cancer tumor cells actively shed extracellular vesicles containing a cargo of proteins, lipids and nucleic acids into the tumor microenvironment and bodily fluids. Because these vesicles are present in elevated levels in the blood, exhibit stability and reflect the cell of origin, there is potential for use in the diagnosis and monitoring of progression of a wide variety of cancers like but certainly not limited to bladder, prostate, brain and renal cancers.
For Cardiovascular disease, the number 1 death cause in Singapore and rapidly on the rise in Asia, it has been established that Acute Coronary Syndrome (heart attack) can be diagnosed based on the content of plasma extracellular vesicles that changes within hours of onset of the symptoms (5). Next to this, prediction of secondary cardiovascular events (a second heart attack or stroke after having a first heart attack or stroke) is done based on plasma extracellular content. The vesicle content predicts better who is at high risk for a second cardiovascular event then all known risk factors together (6).
Extracellular vesicles: a new sample type
Extracellular vesicles, contains miRNAS, proteins and metabolites and can function as a new sample type for biomarker studies. This is important as the USA Suppreme court in the Mayo vs Prometheus case decided in 2012 that measuring the variation of biomarkers under the influence of a disease process and/or therapy is a natural principle that is not patentable. A patent/claim that focuses on use of a natural principle must also include additional (non-conventional) elements to show that the inventor has practically applied, or added something significant to the natural principle itself like a specific sample type (vesicles, miRNAs). For this, we expect an increased interest in extracellular vesicles for biomarker studies as it will be able to translate new vesicle based biomarker findings into the clinic as it is supported by a strong patent position.
Extracellular vesicles have therapeutic value. As carriers of significant amounts of proteins including enzymes and miRNA having a physiological bi-lipid membranes and small size are ideal for crossing the plasma membrane either by membrane fusion or micropinocytosi (7,8).
Stemcells and especially mesenchymal stemcells (MSC) were seen as the core for the replacement therapy in regenerative medicine. The discrepancy between the paucity of MSC engraftment and differentiation, and functional recovery of the targeted tissue has consequently led to the proposal that the therapeutic efficacy of MSC was mediated by the secretion of factors that could reduce cellular injury and enhance repair (9). This increasingly popular paradigm shift is evidenced by the shift in the rationale to trophic secretion for 65 of the 101 MSC clinical trials in 2010 (10).
Evidence is now accumulating that exosomes are the biological therapeutic active component of MSC secretion (4) opening the road to possible therapeutic applications in a large number of diseases like cardiovascular disease, graft vs host and wound healing.
- Tushuisen et al Arterioscler Thromb Vasc Bili 2011;31;4-9.
- Del Conde I, et al, Blood. 2005 Sep 1;106(5):1604-11.
- Th’dry C, et al Nat Rev Immunli. 2009 Aug;9(8):581-93.
- Lai RC, et al Stem Cell Res. 2010;4:214-222.
- Kanhai DA, et al 2013 Am. J. Cardili. In press
- de Hoog VC, et al 2013 Eur. Heart J.: Acute Cardiov. Care. In press
- Lai, RC, SS Tan, et al. Int J Proteomics 2012: 971907
- Lai, RC, TS Chen, et al. 2011, Regen Med 6(4): 481-492
- Caplan, Al and Dennis JE. 2006, J Cell Biochem 98(5): 1076-1084.
- Ankrum, J & Karp JM. 2010, Trends Mli Med 16(5): 203-209.
Extracellular Vesicles and Coagulation
Coagulation is an important process that makes the blood cloth. It stops the damaged blood vessel from bleeding but is also involved in clothing the blood vessels providing blood to the heart or brain leading to a heart attack or stroke.
Coagulation can be activated in several ways but Tissue Factor is a very important activator of blood clothing.
Recently it was found that the blood contains Tissue Factor and that this Tissue Factor is found in blood extracellular vesicles that, among others, originate from monocytes. This identifies extracellular vesicles as an important determinant in blood coagulation in physiological but also pathological processes.
Extracellular Vesicles and Therapy
Since plasma extracellular vesicles contain protein and RNA that originates from the cell of origin, these vesicles probably contain information of the status of the cell of origin.
It is now established that plasma vesicle number, species but also content contains information that can be used in diagnosis and prognosis of disease.
Extracellular Vesicles as “Garbage Collectors” or Communicators
Plasma extracellular vesicles were considered as the “garbage bags” or communicators of the cells released in the plasma for removal.
This view has recently changed dramatically.Extracellular vesicles contain proteins and RNA (miRNA) and it is established that they are actively involved in the communication between cells and tissues in biological processes as inflammation, coagulation and tissue repair.
Extracellular Vesicles as Biomarker Source
Mesenchymal stem cells (MSCs) are known for their beneficial effects to repair damaged tissue. It is now clear that these MSCs secrete extracellular vesicles that have therapeutic potential that can be used as an “off the shelf” therapy in contrast to cell therapy.
Examples of applications investigated are: myocardial ischemia reperfusion injury, heart failure, skin wound healing and graft vs host disease.