Circulating or extracellular microRNAs in biofluids is an emerging class of biomarkers with the great advantage of being minimally invasive in diagnostic use. These microRNAs originate from various circulating cells or from tissue cells including cells shed from organs and cancers (dying cells & apoptotic bodies). microRNAs have been shown to be stabilized and protected from RNase degradation by inclusion in various protein complexes and membranous particles such as exosomes or microvesicles.
Exosomes are nano-sized extracellular vesicles of endocytic origin participating in cell-to-cell communication. Their proposed role as intercellular hormone like messenger together with their stability as carrier of proteins and RNA makes them ideal in the search for biomarkers for a variety of biological questions. Exosomes are released by many cell types and found in many biofluids including serum, plasma, CSF and urine.