The endothelium is more than just a barrier between the bloodstream and the vascular wall; it is an active component involved in numerous processes, including regulation of vascular tone, growth and migration of the underlying smooth muscle cells, and maintenance of vascular structure.18 Under physiological conditions, endothelial cells present an anti-adherent and anti-coagulant surface; but in response to damage, the molecules expressed on their surface can be modified and thus increase cell adhesion capacity. Platelets bind to the damaged surface initiating the coagulation process with the consequent development of inflammation and thrombosis, causing cardiovascular events. Hence, endothelial damage can be the initial event that triggers the appearance of different cardiovascular pathologies11 (Fig. 2).

Fig. 2.

Vascular damage. Oxidative stress and inflammation, among other factors, generate endothelial deterioration leading to: increased adhesion capacity that causes thrombosis, increased EV release and increased leukocyte extravasation, which favors the development of cardiovascular disease. Figure elaborated with Biorender.

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There are different mechanisms involved in the deterioration of the endothelium; the most important in patients with CKD are described below.

Oxidative stress

Oxidative stress is defined as the accumulation of oxidizing molecules, mainly reactive oxygen species (ROS), either by an increase in their production or by a decrease in the antioxidant mechanisms. ROS have a high oxidative capacity and can therefore alter different molecules (proteins, lipids, nucleic acids, etc.) in the cells, causing damage.19,20 In early stages of CKD, it has been observed a correlation between high levels of oxidative stress and disease progression.21,22 Furthermore, patients with CKD accumulate uremic toxins in their bloodstream, including IS (indoxyl sulfate), MDA (malondialdehyde) and ADMA (asymmetric dimethylarginine), which worsen the oxidative stress.23

In general, oxidative stress can be produced by various causes (Fig. 3). In patients with CKD, mainly those with diabetic nephropathy, there is mitochondrial dysfunction that leads to increased ROS production. Studies in animal models and in vitro studies, have shown that in the presence of IS there is an increase in the activity of the enzyme NADH oxidase 4 (NOX4), which leads the generation of larger amounts of ROS.23

Fig. 3.

Main causes of oxidative stress in CKD patients. Oxidative stress results in the generation of damage at the genomic level and activation of proinflammatory pathways. NOX4: NADH oxidase 4 enzyme.

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ROS also alter cellular structures and metabolic pathways. One of the markers used to measure oxidative stress are the so-called AGEs (advanced glycation end products). AGEs bind to their RAGE receptors (receptor system for AGE) and signal through the MAP kinase (MAPK) pathway. Activation of MAPKs allows internalization of the p65 subunit of NF-κB (nuclear factor kappa B) into the nucleus and consequently, increases the release of proinflammatory cytokines and enzymes, and also increase the expression of adhesion molecules.24 At the same time, activated pro-inflammatory immune cells, release oxidative compounds, thus generating a vicious cycle that exacerbates oxidative damage.25

Increased oxidative stress damages DNA. Guanine in particular can be oxidized and transformed into 8-hydroxy-2′-deoxyguanosine (8-OH-dG), which is another marker used to measure oxidative stress.26 These changes in DNA bases generates cellular damage and has been associated with multiple chronic and degenerative diseases, including CKD and carcinomas.27 In addition, there are numerous factors that gradually increase in CKD due to the deterioration of renal function, and these factors are considered to be responsible for the increase in oxidative stress (Table 1).

Table 1.

Oxidative stress associated to CKD.

Parameter	Result	Patients	Sample	Reference
GSH	↓ In patients with moderate or severe CRF in preD.	31 HC83 patients with mild chronic renal failure (CRF) in pre-D,55 patients with moderate CRF in preD47 patients with severe CRF in preD18 HD patients	WB	28
GSSG	↓ In HD compared to HC and severe CRF
GSH-Px activity	↑ In all preD compared with HC		E
GSSG-Red activity	↑ In all preD compared to HC↓ In HD than in patients with severe CKD in preD
GSH-Px activity	↓ Gradually as renal failure progresses in preDCAPD↓ In HD and CAPD		Plasma
GSSG-Rd activity	↑ In HD and CAPD patients compared to HC and patients with severe CRF inpreD
SOD activity	↓ In HD patients		E
MDA	↑ In patients with CKD compared to HC,but are maintained once the disease is started	31 HC 73 patients with mild CRF53 withmoderate CRF36 with advanced CRF	Plasma	29
GSH-Px activity	↓ According to progression of renal damage
AOPP	↑ In patients with moderate and advanced CKD
AGE-pentoside	↑ As renal damage progresses
CRP	↑ In patients with CKD	70 HC60 CKD patients	Plasma	30
Thiols	↓ In CKD patients
Carbonyls	↑ In CKD patients
F2-isoprotans	↑ In CKD patients
IL-6	↑ In CKD patients
ROS	↑ In CKD patients	21 CS PBMNs 22 patients with CKD in stages 1 and 2	PBMNs	31
NADPH oxidase activity	↑ In CKD patients
AOPP	↑ In HD compared to PD	1539 HD patients556 PD patients	Serum	32
Vitamin C	↓ In CKD and even lower in HD patients	38 HC51 patients with CKDstages 3–550 HD	Plasma	33
Zinc	↓ In CKD and HD compared to HC		E
SOD activity	↓ In HD patients
XO activity	↑ In CKD and even more in HD
MDA	↑ In HD

AGE: advanced glycation products; AOPP: advanced glycation protein products; CAPD: continuous ambulatory peritoneal dialysis; HC: healthy controls; PD: peritoneal dialysis; E: erythrocytes; CKD: chronic kidney disease; CRF: chronic renal failure; GSH: glutathione; GSH-Px: glutathione peroxidase; GSSG: glutathione disulfide; GSSG-Red: glutathione reductase; HD: hemodialysis; IL-6: interleukin 6; MDA: malondialdehyde; PBMN: peripheral blood mononuclear cells; CRP: C-reactive protein; preD: predialysis; ROS: reactive oxygen species; WB: whole blood; SOD: superoxide dismutase; XO: xanthine oxidase.

Hyperphosphatemia, present in many patients with CKD, also plays an important role in vascular deterioration and it is related to oxidative stress. In vitro experiments with endothelial cells showed that high phosphate concentrations generate an increase in oxidative stress and a drop in nitric oxide (NO). Under pathological conditions there is a decrease in NO synthesis as a consequence of inhibition of the phosphorylation of the endothelial nitric oxide synthase (eNOS).34 Under physiological conditions NO is released by endothelial cells to produce vascular relaxation and prevent arterial stiffness, so that a decrease in its production favors endothelial deterioration. These results have been corroborated by experiments carried out in healthy and CKD mice: diets with a high content of phosphate promote inflammation and endothelial dysfunction, in addition to a loss of permeability between endothelial cells.35

Numerous studies show how oxidative stress is directly related to proinflammatory factors.36–38 Patients on HD may show an increase of up to 30–40 times the physiological concentration of acetate after the completion of the dialysis session, acetate is the most frequent buffer used in dialysis fluids. This elevation in blood acetate is associated with an increase in oxidative stress, as well as with an increase in some proinflammatory cytokines such as interleukins 1 and 6 (IL-1 and IL-6) and with the synthesis of NO.36–38 If there is also a high concentration of magnesium in the dialysis fluid (1.25 or 2mM), the in vitro production of ROS and MDA increases, although this increase in magnesium has been seen able to prevent an increase in oxidative stress when citrate is used instead of acetate as in dialysis fluids (citrate alone or with a mixture of citrate and a small amount of acetate).16 The increase in the concentration of oxidized glutathione as a result of HD means that the dialysis technique is considered a risk factor associated with an increase in oxidative stress.39

Thus, in patients with CKD uremia triggers an increase in oxidative stress that particularly affects endothelial cells due to their direct contact with blood. In turn, this oxidative stress generates alterations that will favor the development of inflammatory processes; in such a way that the coexistence of inflammation and oxidative stress will trigger and enhance endothelial dysfunction in patients with CKD.

Inflammatory mediators and immune response in CKD

Inflammation plays an important role in the increased risk of cardiovascular events in patients with CKD. It has been shown that inflammatory processes are triggered by factors such as HTN, advanced age, DM, obesity, hyperuricemia, dyslipidemia, smoking, male sex, and family history of CVD.40 Similarly, both the accumulation of uremic toxins and also dialysis procedure required to remove uremic toxins promote the development of inflammation.40,41

Patients with CKD present chronic inflammation caused by uremia and dialysis techniques.42 These inflammatory processes in dialysis patients are more frequent in advanced stages of the disease. Particularly important is the continuous damage of the peritoneum produced during PD that produces the activation of genes related to adaptive immunity and the Th2 lymphocyte response.43 Regarding HD, the use of non-biocompatible membranes or the possible contamination of the dialysis fluid, among other factors,44 will trigger the activation of monocytes, which release proinflammatory cytokines. However, the presence of inflammation in pre-dialysis patients tell us that indicates monocyte activation is not the main cause of inflammation.45–47

At the onset of CKD, patients present low-intensity systemic inflammation which, when prolonged over time, leads to a deterioration in the general condition of the organism and favors the appearance of secondary pathologies such as CVD.48 It is observed a slight elevation of inflammatory markers such as C-reactive protein (CRP) and some cytokines such as IL-6 and tumor necrosis factor α (TNF-α)49; CRP can even be considered a marker of mortality, it has been observed that lower levels of CRP are associated with a lower risk of mortality in HD patients.50 Nevertheless, IL-6, IL-1 and TNF-α are directly related to the severity of CKD. IL-6 has been described as a predictive marker of atherosclerosis, since it contributes to the generation and development of atheroma plaque by various mechanisms.51 The specific signaling pathways used by IL-6 in the development of arteriosclerosis are unknown. In animal models it has been observed that upon binding IL-6 to its receptor IL6-R, the IL-6 trans signaling pathway is activated, which triggers a chronic inflammatory process and favors the formation of atheroma plaque, and therefore, the development of cardiovascular disease.52 IS can bind to the aryl hydrocarbon receptor (AhR) of monocytes to stimulate the secretion of TNF-α. Then TNF-α interacts with endothelial cells increasing the expression of the chemokine CX3CL1 (also known as fractalkine), whose receptor is CX3CR1, is abundant in CD4+CD28− T lymphocytes. This subpopulation of T lymphocytes is elevated in patients with CKD and, if stimulated through the T-cell receptor (TCR), can induce apoptosis in endothelial cells and accelerate the progression of CVD in these patients53 (Fig. 4).

Fig. 4.

Endothelial dysfunction and vascular calcification generated by IS binding to the AhR receptor on monocytes. The increase in TNF-α generated by IS generates an increase in the production of the chemokine CX3CL1 in endothelial cells. When CX3CL1 binds to its receptor on the T lymphocyte, and the T lymphocyte has its T cell receptor active, it will generate the development of endothelial cell apoptosis. AhR: aryl hydrocarbon receptor; BMP2: bone morphogenic protein 2; IS: indoxyl sulfate; MSX2: Msh homrbox protein 2; Runx2: runt-related transcription factor 2; TCR: T-cell receptor; TNF-alpha: tumor necrosis factor alpha; TNFR: TNF receptor.

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TNF-α is one of the main activators of RANKL (receptor activator ligand for nuclear factor κB). Thus, TNF-α in the bone tissue of patients with CKD can activate osteoclasts, altering bone structure and increasing the risk of fractures, which explains the high frequency of fractures in patients on HD.54 Furthermore, the activation of osteoclasts prompts an increase in blood levels of calcium and phosphate which facilitates the mineralization processes of vascular cells. TNF-α potentiates this mineralization process since it allows the translocation of NF-κB, increases the release of EV (which in renal patients contain high levels of calcium) and increases the levels of bone morphogenic protein 2 (BMP-2), inducing osteogenic differentiation and calcification of vascular smooth muscle cells (VSMC).55

In patients with CKD, activated endothelial cells also express a greater amount of VEGF (vascular endothelial growth factor) which, in turn, promotes angiogenesis and vessel remodeling to counteract renal tissue hypoxia. Likewise, in patients who present proteinuria due to a decrease in glomerular filtration, it has been seen that the endothelial cells of the glomerulus increase the release of VEGF.56,57

Aging is defined as a functional decline of the organism that usually involves morphological and physiological changes that entail a loss of homeostatic reserves.88 There are two types of aging: physiological aging and premature or accelerated aging associated with pathologies. Physiological aging is the consequence of time passing by and is therefore closely related to age. When aging appears early and together with the development of diseases associated with aging, it can be identified as premature aging associated with diseases. Thus, renal patients show accelerated aging, since many of them suffer ahead of time diseases associated with aging, such as CVD.4,18,89 Premature aging in these patients can be associated with the accumulation of senescent cells, those that have lost their ability to proliferate. Cellular senescence is defined as a process that takes place as a consequence of cell damage caused by multiple reasons (oxidative stress, proinflammatory cytokines and/or EV), the end result of which is that cells lose their ability to divide, do not die and contribute to the development of age-associated diseases. Among other changes, they are cells that present increased ROS, accumulation of dysfunctional mitochondria, decreased condensation of constitutive heterochromatin with loss of lamin β and increased β-galactosidase lysosomal enzyme activity.88 In addition, senescent cells show a deficit in protein synthesis, as well as an increase in their degradation. Obviously, an increase in senescent cells in a tissue triggers tissue dysfunction.

In patients with CKD, cellular senescence occurs in response to the damage generated by the action of the uremic toxins accumulated during the progression of the disease.90,91 The accelerated cellular senescence attributed to uremia generates an increase in oxidative stress that in turn causes deterioration of cellular structures. As a result, intracellular signals are produced that cause the cell to acquire a senescent phenotype.48 At the systemic level, senescent cells release pro-inflammatory factors that, if persisted over time, generate a generalized deterioration of the organism. This deterioration favors the appearance of tumoral processes and degenerative and chronic illnesses.92

The renal cells are responsible for producing the Klotho protein, an enzyme capable of hydrolyzing the beta-glucurinide steroid. It is a protein with an anti-aging effect, capable of modulating stress-induced senescence and functional response. The decrease in intracellular levels of Klotho has been associated with endothelial senescence, while exogenous Klotho prevents cellular senescence by inhibiting the increase in oxidative stress induced by uremia, as well as inactivating NF-κB and inhibiting its ability to bind to DNA. In this way, the NFκB/IκB complex is stabilized and the release of cytokines that participate in inflammatory processes is reduced. When the levels of this protein are reduced due to uremia, there is an increase in oxidative stress and endothelial senescence is greater.93,94 It has been observed that the α-Klotho protein plays a fundamental role in the maintenance of the integrity and homeostasis of the endothelial cells. Specifically, the functions that have been attributed to α-Klotho are the suppression of the expression of adhesion molecules such as ICAM and VCAM, the attenuation of the NF-κB signaling pathway, and the prevention of hyper-permeabilization95 and apoptosis of endothelial cells by mediating the internalization of the complex formed by the canonical transient potential receptor 1 (TRPC1) and the vascular endothelial growth factor receptor 2 (VEGFR2).96 Patients with CKD present a deficiency of this protein which is due to multiple factors.19 This deficit could explain, at least in part, the greater risk of these patients of suffering CVD. In addition, it has been demonstrated that Klotho, together with the fibroblast growth factor 23 (FGF23) is essential in the axis bone-kidney, since Klotho maintains the homeostasis of the phosphate, collaborating in some way with FGF23 by optimizing the binding of FGF23 to its receptor (possibly it should be under one same route of signaling inhibiting the reabsorption of phosphate), since the degradation of FGF23 leads to a deterioration of the renal function with hyperphosphatemia.94

Finally, it should be emphasized again that endothelial damage is a previous step in the development of several CVDs. The CVD associated with the CKD is partly determined by a rigidity of the blood vessels caused by a state of inflammation and a loss of balance between the pro-aging and anti-aging systems, which finally triggers a process of vascular calcification. At the vascular level, it is observed that patients with CKD present an aged vascular tissue, similar to that found in healthy individuals of advanced age.64

The most prevalent vascular alteration in patients with advanced CKD is vascular calcification, and in many cases it is not detected until the damage is irreversible. Vascular calcification is due to the increase in bone morphogenic proteins and the presence of a high calcium content. The increase in Ca and P in plasma augment the expression of proteins involved in bone formation such as osteopontin, osteocalcin, certain proteoglycans and BMP-2, as well as other factors involved in vascular calcification.12 There are two types of calcifications: 1) calcification of the tunica media, also known as Mönckeberg sclerosis, which affects the VSMC and elastic fibers, which harden and lose their capacity of distension,108 and 2) atherosclerotic calcification of the tunica intima, which is associated with deposition of lipid and lipoprotein followed by calcium accumulation under the tunica intima.109 This deposition can stimulate the development of both innate and adaptive immune responses, inducing the expression of pro-inflammatory molecules in both endothelial cells and VSMC, which stimulates the infiltration of monocytes/macrophages into the tissues. Both types of vascular calcifications are very common in ACKD and may coexist in the same vessel.

The hyperphosphatemia and hypercalcemia are two of the main promoters associated with the development of vascular calcification in the CKD.14,108 The development of calcifications is promoted in patients receiving treatment with vitamin D together with oral calcium salts and who have a positive calcium balance during the dialysis session.110 In vitro models have shown that the increase in phosphorus favors the transformation of VSMC into osteogenic cells, with production of extracellular matrix and subsequent mineralization. Therefore, hyperphosphatemia and hypercalcemia not only passively generate deposits, but also intervene in a highly regulated process by which VSMC differentiate into osteoblasts.111 Eventually, the decrease in the renal function causes blood accumulation of phosphate which, together with the deficiency of circulating inhibitors of calcification and the poor local production of these inhibitors, favors calcification through the activation of Toll-like receptor 4 (TLR-4), which in turn stimulates the expression of NF-κB in VSMCs and leads to an increase in the release of proinflammatory cytokines.14,112

In vitro studies have shown that uremic toxins derived from guanidine (asymmetric dimethylarginine (SDMA), guanidinobutyric acid (GAB), guanidine (G) and guanidino acetic acid (GAA)) are capable of stimulating osteoclastogenesis.113 Uremia also favors the secretion of the osteoblast differentiation factor, Cbfa1, together with an increase in the expression of osteogenic proteins.107,114 In VSMCs the IS stimulates proliferation and favors the production of TGF-β which participates in fibrosis processes.115 Also, the increase in oxidative stress –which is observed in patients with CKD– is closely associated with the development of vascular calcification mediated by the expression of Runx2 (runt-related transcription factor 2) in VSMCs.108 Therefore, various stimuli, such as increased ROS, proinflammatory chemokines and cytokines (CCL5, CCL2, TNF-α, IL-6), and high phosphorus and calcium levels, will facilitate the entry of NF-kB into the core of VSMCs, which stimulates the production of factors involved in calcification (Runx2, OPN, Msh homrbox protein 2 (MSX2), alkaline phosphatase, BMP2) (Fig. 4). In addition, calcium helps to release of EVs, which reinforces the calcification process.107,115–117 VSMCs themselves release a greater amount of EV in response to stress induced by ambient calcium, which also favors vascular calcification.118

In addition, senescence also plays a key role in the development of vascular calcification. It has been observed that EVs released by macrophages of aged individuals participate in the calcification of the vascular matrix.104 Endothelial MVs found in plasma of elderly subjects and released by senescent endothelial cells also help in the calcification of VSMCs, since they contain high levels of calcium, phosphates molecules and proteins that participate in the initiation of calcification.12

Thus, abnormalities in minerals, uremia and the increase in oxidative stress, inflammation and EV release in patients with CKD favor the development of vascular calcification, thereby increasing the risk of suffering cardiovascular damage

Uremic toxins, among which IS and p-cresol stand out, cause damage of endothelial cells, generating a proinflammatory state. This continuous damage of endothelial cells stimulate the release of a greater amount of endothelial MV, which in turn modify vascular tone and further increase vascular damage, thus generating a vicious cycle.11,59,121–123 These endothelial MV are involved in the pathogenesis of several CVD, including atherosclerosis.11,124 There is a general relationship between renal function and cardiovascular risk, which is reflected in excessive production of endothelial vesicles that could act as a marker of endothelial dysfunction.

It has been described that endothelial MV promote vascular calcification, since treatment of VSMC with endothelial VM from endothelial cells previously treated with IS induced calcification in VSMC, whereas endothelial MV from endothelial cells not treated with uremic toxins did not produce calcification.107

Platelet MV are another type of MV implicated in the development of CVD. In this pathological process there is excessive platelet activation which is followed by platelet aggregation, secretion of their internal granules and release of a greater number of MV, all of which have procoagulant activity.120 Moreover, in a situation of endothelial dysfunction, platelets tend to adhere to the damaged surface,125 with the consequent release of potent mitogenic factors leading to the proliferation of VSMs and the progression of vascular damage.

The dialysis technique itself may be a risk factor for renal patients. There are several studies that show hypercoagulation in these patients, probably due to increased expression of tissue factor (TF).126 TF, also known as thromboplastin, is expressed in the cell membrane and is synthesized by different cell types; and, it can be found on the surface of monocytes and endothelial cells in inflammatory states. This factor is involved in local thrombi formation. TF is expressed on the surface of EV, so it can bind to the platelet surface of an evolving thrombus, which occurs frequently in uremic patients.127 Likewise, it has been shown that elevated levels of TF, important in thrombogenic activity, can be crucial in patients undergoing some types of RRT.11 This suggests that EVs expressing TF may be biomarkers of thrombotic events in uremic patients.127

In recent years, the analysis of EV in body fluids has been used as a diagnostic tool (biomarker) in various pathologies, this is the case of patients with CVD associated to CKD.40,128 Biomarkers are an analytical tool that provides objective, measurable and evaluable information on biological function, some pathological processes or the response to treatment. Biomarkers are essential in clinical practice because they allow early identification of a given pathology, and thus allow early therapeutic intervention that prevent the development of such pathology and the possible negative consequences for the individual.11 In general, high levels of EV have been detected in numerous pathologies, particularly those of a chronic and inflammatory nature, such as diabetes, hypertension, cancer and CKD.129

In the context of CKD, a relationship has been observed between renal function and cardiovascular risk, all of which is reflected in an elevated production of endothelial vesicle that could act as a marker of endothelial dysfunction.105 Specifically, Mezentsev et al. described that the physiological levels of endothelial MV in healthy individuals is between 103–104MV/mL, while in individuals with CVD it is 105MV/mL.130 Different studies point to the existence of a higher concentration of circulating EV in patients with CVD such as congestive heart failure, coronary artery disease, peripheral vascular disease and cerebral ischemia.60

In uremic patients there are also high levels of platelet MV with a procoagulant effect, which can be associated with coagulation disorders, cerebrovascular accidents, unstable angina and acute myocardial infarction. This explains its possible contribution to the development of CVD (especially associated with thrombosis and platelet instability) and its use as a possible diagnostic biomarker.131,132 The levels of platelet MV in patients on HD and PD were higher than in healthy people; and even more increased than in those patients who suffered a thrombotic event.131 It has also been observed that patients with CKD who have suffered an acute myocardial infarction – and therefore with a high risk of suffering a new thrombotic event – have a high levels of platelet MV and that the levels of platelet MV are higher in those patients with a more advanced CKD.133 These platelet MVs express P-selectin, which indicates platelet activation. In addition, as mentioned above, the increase in VE with TF can be a clinical marker of risk of thrombotic event in patients with CKD.127

It has been proposed that EVs and their content may act as therapeutic targets. Firstly, since CVD has been related to the increased release of EVs, pharmacological strategies can be designed to inhibit the release EVs and even their interaction with the target cells. For example, ceramide which is an important component in exosome biogenesis can be inhibited.63 Even so, treatments focused on the inhibition of EV release are scarce, due to the lack of specific knowledge of the mechanisms involved in the biogenesis and release of EVs.11 Treatments focused on reducing EV release could reduce the morbidity and mortality of patients with CKD.63

It has been observed that some drugs that have been used traditionally in the treatment of CVD and CKD modulate the release of EV (Table 3).

Studies have been performed to test whether endothelial MV levels could be modulated by drugs. For example, the use of statins, specifically atorvastatin, produced a decrease MV and VEGF levels.134 This is possible because statins inhibit the Rho-kinase pathway which is involved in skeletal reorganization and MV release, thus the release of MV is reduced (not only endothelial MV but also those derived from platelets and leukocytes).135,136 Furthermore, in patients with hypertension and type 1 DM, treatment with simvastatin together with losartan has been observed to decrease plasma concentrations of endothelial, platelet and monocyte-derived MV.135 Aspirin could also have a reducing effect on EV release, specifically on endothelial and platelet, but the results are somewhat heterogeneous.11,129 A reduction in peripheral blood endothelial MV was also observed in an animal model of hypertension in which antihypertensive drugs (aliskiren, nerbivolol and olmesartan) were used; this reduction also mediates the antiangiogenic effects of these drugs.137

Antioxidants such as vitamin C could also reduce the release of VE; specifically, in patients with type 1 DM and dislipemia after suffering a myocardial infarction.11

In addition to using EVs as a target for treatments, it has recently been investigated the use of EVs as a therapeutic tool, as a way to deliver a treatment in a more effective and “physiological” manner. This idea arises from the fact that EVs under physiological conditions may have beneficial effects on target cells. For example, it has been observed that EVs may be involved in tissue repair and immune modulation processes, therefore they could be used directly as therapeutic agents in regenerative medicine and the treatment of autoimmune diseases.63

Under physiological conditions, platelet-derived MVs are capable – through VEGF – of stimulating proliferation, survival, cell migration and the formation of new capillaries. Additionally, the endothelial MV are related with to regenerative processes and the maintenance of vascular homeostasis; therefore, an increase in the levels of this type of vesicle is key in processes where vascular regeneration is taking place.11,120

Regarding the kidney, models of diabetic nephropathy, CKD, fibrosis and acute kidney injury, have shown that EV derived from mesenchymal stem cells have a renoprotective function. In general, EVs derived from stem cells are the ones that present the greatest beneficial effects in kidney diseases. This could be due to its content rich in miRNAs and proteins (mainly related to cell proliferation, migration and adhesion).63

Finally, the use of EVs as a vehicle for treatments (which could be drugs, miRNAs or proteins) has also been explored. This type of delivery has the advantage that they are less immunogenic and cytotoxic, and up to now the evidence is that they seem to have less rejection than nanoparticles.63