Virtually all cells in the organism secrete extracellular vesicles (EVs), a heterogeneous population of lipid bilayer membrane-enclosed vesicles that transport and deliver payloads of proteins and nucleic acids to recipient cells, thus playing central roles in cell-cell communications. Exosomes, nanosized EVs of endosomal origin, regulate many pathophysiological processes including immune responses and inflammation, tumour growth, and infection. Healthy subjects and patients with different diseases release exosomes with different RNA and protein contents into the circulation, which can be measured as biomarkers. The discovery of exosomes as natural carriers of functional small RNA and proteins has raised great interest in the drug delivery field, as it may be possible to harness these vesicles for therapeutic delivery of miRNA, siRNA, mRNA, lncRNA, peptides, and synthetic drugs. However, systemically delivered exosomes accumulate in liver, kidney, and spleen. Targeted exosomes can be obtained by displaying targeting molecules, such as peptides or antibody fragments recognizing target antigens, on the outer surface of exosomes. Display of glycosylphosphatidylinositol (GPI)-anchored nanobodies on EVs is a novel technique that enables EV display of a variety of proteins including antibodies, reporter proteins, and signaling molecules. However, naturally secreted exosomes show limited pharmaceutical acceptability. Engineered exosome mimetics that incorporate desirable components of natural exosomes into synthetic liposomes or nanoparticles, and are assembled using controllable procedures may be more acceptable pharmaceutically. In this communication, we review the current understanding of physiological and pathophysiological roles of exosomes, their potential applications as diagnostic markers, and current efforts to develop improved exosome-based drug delivery systems.

EVs are the active component of the paracrine secretion by human CPCs. As a cell-free approach, EVs could circumvent many of the limitations of cell transplantation.

The endothelium holds a pivotal role in cardiovascular health and disease. Assessment of its function was until recently limited to experimental designs due to its location. The advent of novel techniques has facilitated testing on a more detailed basis, with focus on distinct pathways. This review presents available in-vivo and ex-vivo methods for evaluating endothelial function with special focus on more recent ones. The diagnostic modalities covered include assessment of epicardial and microvascular coronary endothelial function, local vasodilation by venous occlusion plethysmography and flow-mediated dilatation, arterial pulse wave analysis and pulse amplitude tonometry, microvascular blood flow by laser Doppler flowmetry, biochemical markers and bioassays, measurement of endothelial-derived microparticles and progenitor cells, and glycocalyx measurements. Insights and practical information on the theoretical basis, methodological aspects, and clinical application in various disease states are discussed. The ability of these methods to detect endothelial dysfunction before overt cardiovascular disease manifests make them attractive clinical tools for prevention and rehabilitation. METHODS FOR EVALUATING ENDOTHELIAL FUNCTION. A POSITION STATEMENT FROM THE EUROPEAN SOCIETY OF CARDI-OLOGY WORKING GROUP ON PERIPHERAL CIRCULATION. John Venous occlusion plethysmographyVenous occlusion plethysmography (VOP), established more than 100 years ago, is the longest living method for investigating blood flow in humans. Flow-mediated dilatationConduit vessels respond to alterations in blood flow by increasing vessel diameter via an endothelial dependent mechanism. 20,21 The flow-mediated dilatation (FMD)technique measures changes in conduit artery diameter by ultrasound. This response has been shown to reflect local bioactivity of endothelial-derived NO. 22 MethodologyThe brachial artery is most often imaged (online Supplemental Figure 2). FMD studies are performed in a quiet temperature controlled room while subjects are lying supine for >10 min prior to image acquisition. A straight, non-branching segment of the brachial artery above the antecubital fossa is imaged in the longitudinal plane with the ultrasound probe securely fixed using a stereotactic clamp. This permits fine adjustments in the coronal and sagittal planes. A blood pressure cuff is placed 1-2 cm below the antecubital fossa and inflated to supra-systolic pressure. 23 After cuff release, reactive hyperaemia results and is quantified using Doppler. The arterial diameter is recorded at end diastole using electrocardiographic gating during image acquisition, to determine the response of the conduit artery to increase in flow. 24 Changes in the arterial diameter are assessed using commercial digital edge detection software. Pulse wave analysisThe arterial waveform contains important information about the stiffness of the large arteries and amount of wave reflection within the arterial system. 32 Wave reflection occurs at sites of impedance mismatc...