Augmentation of endothelin-1, prostacyclin and thromboxane A2 secretion associated with in vitro ageing in cultured human umbilical vein endothelial cells

Pathophysiology of deep vein thrombosis

Deep venous thrombosis is a frequent, multifactorial disease and a leading cause of morbidity and mortality. Most of the time deep venous thrombosis is triggered by the interaction between acquired risk factors, such as hip fracture, pregnancy, and immobility, and hereditary risk factors such as thrombophilias. The mechanisms underlying deep venous thrombosis are not fully elucidated; however, in recent years, important advances have shed light on the role of venous flow, endothelium, platelets, leukocytes, and the interaction between inflammation and hemostasis. It has been described that the alteration of venous blood flow produces endothelial activation, favoring the adhesion of platelets and leukocytes, which, through tissue factor expression and neutrophil extracellular traps formation, contribute to the activation of coagulation, trapping more cells, such as red blood cells. Thus, the concerted interaction of these phenomena allows the formation and growth of the thrombus. In this work, the main mechanisms involved in the pathophysiology of deep vein thrombosis will be described.

Reconstitution of autophagy ameliorates vascular function and arterial stiffening in spontaneously hypertensive rats

Insufficient autophagy has been proposed as a mechanism of cellular aging, as this leads to the accumulation of dysfunctional macromolecules and organelles. Premature vascular aging occurs in hypertension. In fact, many factors that contribute to the deterioration of vascular function as we age are accelerated in clinical and experimental hypertension. Previously, we have reported decreased autophagy in arteries from spontaneously hypertensive rats (SHRs); however, the effects of restoring autophagic activity on blood pressure and vascular function are currently unknown. We hypothesized that reconstitution of arterial autophagy in SHRs would decrease blood pressure and improve endothelium-dependent relaxation. We treated 14- to 18-wk-old Wistar rats (n = 7 vehicle and n = 8 trehalose) and SHRs (n = 7/group) with autophagy activator trehalose (2% in drinking water) for 28 days. Blood pressure was measured by radiotelemetry, and vascular function and structure were measured in isolated mesenteric resistance arteries (MRAs) using wire and pressure myographs, respectively. Treatment with trehalose had no effect on blood pressure in SHRs; however, isolated MRAs presented enhanced relaxation to acetylcholine, in a cyclooxygenase- and reactive oxygen species-dependent manner. Similarly, trehalose treatment shifted the relaxation to the Rho kinase (ROCK) inhibitor Y-27632 to the right, indicating reduced ROCK activity. Finally, trehalose treatment decreased arterial stiffness as indicated by the slope of the stress-strain curve. Overall these data indicate that reconstitution of arterial autophagy in SHRs improves endothelial and vascular smooth muscle function, which could synergize to prevent stiffening. As a result, restoration of autophagic activity could be a novel therapeutic for premature vascular aging in hypertension.NEW & NOTEWORTHY This work supports the concept that diminished arterial autophagy contributes to premature vascular aging in hypertension and that therapeutic reconstitution of autophagic activity can ameliorate this phenotype. As vascular age is a new clinically used index for cardiovascular risk, understanding this mechanism may assist in the development of new drugs to prevent premature vascular aging in hypertension.

Novel Contributors and Mechanisms of Cellular Senescence in Hypertension-Associated Premature Vascular Aging

Hypertension has been described as a condition of premature vascular aging, relative to actual chronological age. In fact, many factors that contribute to the deterioration of vascular function as we age are accelerated in hypertension. Nonetheless, the precise mechanisms that underlie the aged phenotype of arteries from hypertensive patients and animals remain elusive. Cellular senescence is an age-related physiologic process in which cells undergo irreversible growth arrest. Although controlled senescence negatively regulates cell proliferation and promotes tissue regeneration, uncontrolled senescence can contribute to disease pathogenesis by presenting the senescence-associated secretory phenotype, in which molecules such as proinflammatory cytokines, matrix metalloproteases, and reactive oxygen species are released into tissue microenvironments. This review will address and critically evaluate the current literature on the role of cellular senescence in hypertension, with particular emphasis on cells types that mediate and modulate vascular function and structure.

Vascular endothelial dysfunction and pharmacological treatment

The endothelium exerts multiple actions involving regulation of vascular permeability and tone, coagulation and fibrinolysis, inflammatory and immunological reactions and cell growth. Alterations of one or more such actions may cause vascular endothelial dysfunction. Different risk factors such as hypercholesterolemia, homocystinemia, hyperglycemia, hypertension, smoking, inflammation, and aging contribute to the development of endothelial dysfunction. Mechanisms underlying endothelial dysfunction are multiple, including impaired endothelium-derived vasodilators, enhanced endothelium-derived vasoconstrictors, over production of reactive oxygen species and reactive nitrogen species, activation of inflammatory and immune reactions, and imbalance of coagulation and fibrinolysis. Endothelial dysfunction occurs in many cardiovascular diseases, which involves different mechanisms, depending on specific risk factors affecting the disease. Among these mechanisms, a reduction in nitric oxide (NO) bioavailability plays a central role in the development of endothelial dysfunction because NO exerts diverse physiological actions, including vasodilation, anti-inflammation, antiplatelet, antiproliferation and antimigration. Experimental and clinical studies have demonstrated that a variety of currently used or investigational drugs, such as angiotensin-converting enzyme inhibitors, angiotensin AT1 receptors blockers, angiotensin-(1-7), antioxidants, beta-blockers, calcium channel blockers, endothelial NO synthase enhancers, phosphodiesterase 5 inhibitors, sphingosine-1-phosphate and statins, exert endothelial protective effects. Due to the difference in mechanisms of action, these drugs need to be used according to specific mechanisms underlying endothelial dysfunction of the disease.

Complementary effects of ciclopirox olamine, a prolyl hydroxylase inhibitor and sphingosine 1-phosphate on fibroblasts and endothelial cells in driving capillary sprouting

Capillary sprouting, a key step of neoangiogenesis in wound healing and tumor growth, also represents a therapeutic target for tissue repair. It requires crosstalk between endothelial cells (EC) and other cell types. We studied this process in a microfluidic platform that allows EC to migrate out of a channel across a collagen gel up a gradient of factors produced by a collection of encapsulated fibroblasts. Introduction of a prolyl hydroxylase inhibitor (PHi), ciclopirox olamine (CPX) to stabilize hypoxia inducible factor 1α (HIF-1α) predominantly in fibroblasts induced capillary sprouting in EC, but the most complex tubular networks with true lumina formed after combining CPX with the lysophospholipid sphingosine 1-phosphate (S1P). The enhanced angiogenesis is a possible consequence of the generation of mutually stimulating factors as each cell type responded differently to the compounds. The combination of CPX and S1P induced secretion of vascular endothelial growth factor (VEGF) in fibroblast culture whereas the angiogenic monocyte chemoattractant protein (MCP)-1 was exclusively secreted by fibroblasts, but only in the presence of EC-conditioned medium. Antibody interference with fibroblast-produced VEGF and MCP-1 inhibited the sprouting response. These observations not only demonstrate the collaboration of EC and fibroblasts in inducing capillary sprouting but also suggest that the combination of CPX and S1P enhances angiogenesis and thus might be of therapeutic value for the pharmacological induction of tissue repair and regeneration.

Acute kidney injury in the elderly: pathogenesis, diagnosis and therapy

Elderly patients, especially those with chronic kidney disease, are at least a 3.5-fold higher risk for the development of acute kidney injury (AKI). With aging, renal functional reserve is lower owing to specific cellular changes that affect function. Molecular studies are elucidating these cellular changes and offer the prospect of designing novel therapeutics. The spectrum of AKI in elderly patients is wide but is over-represented by prerenal and postrenal (obstructive) etiologies. This reflects potentially nephrotoxic clinical variables, such as combordid states, impaired baseline renal function, polypharmacy and an increase in high-risk procedures. In this population, the development of AKI can lead to longer hospital stays, higher mortality rates and an increased risk for the development of chronic kidney disease and end-stage renal disease. Careful attention to clinical risk factors, avoidance of nephrotoxic insults and meticulous supportive care for patients who develop AKI is critical in alleviating the burden of this problem.

Bradykinin protects against oxidative stress-induced endothelial cell senescence

Premature aging (senescence) of endothelial cells might play an important role in the development and progression of hypertension and atherosclerosis. We hypothesized that bradykinin, a hormone that mediates vasoprotective effects of angiotensin-converting enzyme inhibitors, protects endothelial cells from oxidative stress-induced senescence. Bradykinin treatment (0.001 to 1 nmol/L) dose-dependently decreased senescence induced by 25 micromol/L of H(2)O(2) in cultured bovine aortic endothelial cells, as witnessed by a complete inhibition of increased senescent cell numbers and a 34% reduction of the levels of the senescence-associated cell cycle protein p21. Because H(2)O(2) induces senescence through superoxide-induced DNA damage, single-cell DNA damage was measured by comet assay. Bradykinin reduced DNA damage to control levels. The protective effect of bradykinin also resulted in a significant increase in the migration of H(2)O(2)-treated bovine aorta endothelial cells in an in vitro endothelial injury model, or "scratch" assay. The protective effect of bradykinin was abolished by the bradykinin B2 receptor antagonist HOE-140 and the NO production inhibitor N(omega)-methyl-L-arginine acetate salt. Therefore, we conclude that bradykinin protects endothelial cells from superoxide-induced senescence through bradykinin B2 receptor- and NO-mediated inhibition of DNA damage.

Vascular cell senescence: contribution to atherosclerosis

Cardiologists and most physicians believe that aging is an independent risk factor for human atherosclerosis, whereas atherosclerosis is thought to be a characteristic feature of aging in humans by many gerontologists. Because atherosclerosis is among the age-associated changes that almost always escape the influence of natural selection in humans, it might be reasonable to regard atherosclerosis as a feature of aging. Accordingly, when we investigate the pathogenesis of human atherosclerosis, it may be more important to answer the question of how we age than what specifically promotes atherosclerosis. Recently, genetic analyses using various animal models have identified molecules that are crucial for aging. These include components of the DNA-repair system, the tumor suppressor pathway, the telomere maintenance system, the insulin/Akt pathway, and other metabolic pathways. Interestingly, most of the molecules that influence the phenotypic changes of aging also regulate cellular senescence, suggesting a causative link between cellular senescence and aging. For example, DNA-repair defects can cause phenotypic changes that resemble premature aging, and senescent cells that show DNA damage accumulate in the elderly. Excessive calorie intake can cause diabetes and hyperinsulinemia, whereas dysregulation of the insulin pathway has been shown to induce cellular senescence in vitro. Calorie restriction or a reduction of insulin signals extends the lifespan of various species and decreases biomarkers of cellular senescence in vivo. There is emerging evidence that cellular senescence contributes to the pathogenesis of human atherosclerosis. Senescent vascular cells accumulate in human atheroma tissues and exhibit various features of dysfunction. In this review, we examine the hypothesis that cellular senescence might contribute to atherosclerosis, which is a characteristic of aging in humans.

Articular chondrocyte aging and endothelin-1

OBJECTIVE

To compare in cell culture endothelin-1 (ET-1) production, receptor density, and effect on macromolecular synthesis by articular chondrocytes (AC).

METHODS

AC were isolated from 1-month and 18-month old rats and cultured as monolayers. They were incubated with ET-1 without or with iNOS inhibitors, nitro-L-arginine methyl ester (L-NAME) or guanylate cyclase inhibitor, LY83583 and then [3H]thymidine, 35SO4 and [3H]proline incorporations were measured. The density and affinity for 125I-ET-1 of binding sites, and receptor isotypes were determined. The cells were also treated with interleukin-1beta (IL-1beta) or tumor necrosis factor-alpha (TNF-alpha), and then ET-1 productions measured. As well, the cells were challenged with NOC-5 (nitric oxide donor) or ET-1 and then ET-1 and NO respectively were measured.

RESULTS

A concentration-dependent stimulation of DNA, PG, collagen and NO synthesis was obtained when cells were incubated with ET-1 for 24-h. Eighteen-month old chondrocytes incorporated per microg DNA more [3H]thymidine, 35SO4 and [3H]proline but less NO when challenged with ET-1 than the 1-month old cells. However, strong inhibition of this initial stimulation was seen after 48-h. L-NAME and LY83583 enhanced basal-, and ET-1-induced initial stimulation and completely suppressed late (at 48-h to 72-h) ET-1-induced inhibition, suggesting NO was responsible for this inhibitory effect. Eighteen-month old chondrocytes expressed per mug DNA more high affinity receptors of predominantly ET(A) subtype. They also produced more ET-1 but less NO under basal conditions and more ET-1 when challenged with IL-1beta and TNF-alpha. NOC-5 inhibited the production of ET-1.

CONCLUSIONS

Eighteen-month old chondrocytes produce more ET-1, possess more ET-1-specific receptors, and increase more DNA, PG and collagen synthesis when challenged during 24-h with ET-1. NO, which suppresses ET-1 production and the production of which is increased by ET-1, seems to account for the late ET-1-induced inhibition of macromolecular synthesis. The possible implication of ET-1 in aging as related to osteoarthritis is discussed.

Simulated microgravity upregulates an endothelial vasoconstrictor prostaglandin

Endothelial nitric oxide contributes to the vascular hyporesponsiveness to norepinephrine (NE) observed in carotid arteries from rats exposed to simulated microgravity. The goal of the present study was to determine whether a cyclooxygenase product of arachidonic acid also influences vascular responsiveness in this setting. Microgravity was simulated in rats by hindlimb unweighting (HU). After 20 days of HU, carotid arteries were isolated from control and HU-treated rats, and vascular rings were mounted in tissue baths for the measurement of isometric contraction. Two cyclooxygenase inhibitors, indomethacin and ibuprofen, and the selective thromboxane A(2) prostanoid-receptor antagonist, SQ-29548, had no effect on the contraction to NE in control vessels but markedly reduced contraction to NE in HU vessels. When the endothelium was removed, indomethacin no longer had any effect on the NE-induced contraction in HU vessels. In endothelium-intact vessels in the presence of indomethacin, the addition of the nitric oxide synthase inhibitor, N(G)-L-nitro-arginine methyl ester, to the medium bathing HU vessels increased the contraction to NE to the level of that of the control vessels. These results indicate that HU treatment induced two endothelial changes in carotid artery that opposed each other. Nitric oxide activity was increased and was responsible for the vascular hyporesponsiveness to NE. The activity of a vasoconstrictor prostaglandin was also increased, and attenuated the vasodilating effect of nitric oxide.

Endothelin-1 receptors on cultured rat articular chondrocytes: regulation by age, growth factors, and cytokines, and effect on cAMP production

The presence of endothelin-1 receptor proteins and the expression of their specific mRNAs were studied using 1st passage confluent monolayers of articular chondrocytes, isolated from 1-month and 18-month-old rats following 24-h incubation with several growth factors and cytokines. The ET-1- binding sites were predominantly of ETA subtype since BQ123, but not IRL1038 (ETB receptor subtype agonist), effectively blocked 125I-ET-1 binding. The 18-month-old rat cell monolayers bear approximately twice as many 125I-ET-1-binding sites as the 1-month-old rat cells. PDGF, EGF, and IGF-1 increased the number of binding sites in a concentration-dependent manner in both old and young rat cells with PDGF being the most active and EGF more active than IGF-1. IL-1beta, more potently than LPS, increased the number of binding sites in young rat cells only, whereas b-FGF, TGF-beta and GM-CSF had no effect or decreased slightly 125I-ET-1 binding in both types of cells. TNF-alpha strongly decreased the number of binding sites on both young and old rat cells, only. RT-PCR showed an increased expression of the specific ETA mRNA with the age of animals and in the presence of 50 ng/ml PDGF BB only. The incubation of the cells with ETs 1-3 for 10 min resulted in a 50% decrease of cellular cAMP but the blocking of the receptors with BQ123 prior to their exposure to ETs had no effect on cAMP production whereas IRL1038 counteracted this effect only marginally. This suggests a receptor-independent mechanism for ETs-induced inhibition of cAMP production. However, a 10-min co-incubation of cells with ET-1 and with one of the following agents: cholera toxin, pertussis toxin, indomethacin, L-NMA, U73122 and calphostin resulted in an almost complete (calphostin) or partial suppression of ET-1-induced inhibition of cAMP production. The significance of these findings is unclear but the increased density of ET-1 binding sites on old rat cells and its regulation by certain growth factors or cytokines suggest the involvement of ET-1 in aging and possibly in age-related diseases.

Age-associated changes in nitric oxide metabolites nitrite and nitrate

Aging is an important determinant of vascular disease. Endothelial dysfunction accompanying vascular disease may be related to cardiovascular risk factors such as aging, hypertension, and atherosclerosis. Experimental models suggest that endothelium-derived nitric oxide is reduced with aging, and this reduction is implicated in atherogenesis. The aim of this study was to determine whether increased age resulted in altered serum nitrite and nitrate levels, end-products of nitric oxide, in healthy subjects. Sixty-nine healthy individuals were divided into five different age groups: group I (6-15 years), group II (16-30 years), group III (31-45 years), group IV (46-60 years), and group V (>61 years). In these subjects, serum nitrite was measured by the Griess reaction and nitrate by the nitrate reductase method. Statistical analysis showed that serum nitrite levels were not significantly different in any of the groups, while serum nitrate concentrations exhibited significant differences (P<0.001). These findings suggest that nitric oxide synthesis and/or secretion is reduced with age and consequently endothelium-dependent vasodilation is impaired.

Endothelin-1 in monolayer cultures of articular chondrocytes from young and old rats: regulation by growth factors and cytokines

The endothelin-1 (ET-1) concentrations were measured by RIA in the media of confluent monolayer cultures of rat articular chondrocyte (RAC) exposed to fetal calf serum (FCS) and several growth factors and cytokines. The cells were obtained from 1- and 18-month-old rats. First passage cells were starved in Dulbecco's modified Eagle's medium (DMEM) containing 0.2% FCS serum for 24 h and then incubated for 48 h in the same fresh medium with each of the following factors: fetal calf serum (FCS), transforming growth factor-beta (TGF-beta), platelet-derived growth factor (PDGF), epidermal growth factor (EGF), insulin-like growth factor-1 (IGF-1), interleukin-1 beta (IL-1beta), tumor necrosis factor alpha (TNF-alpha), lipopolysaccharide (LPS), and NO donor, sodium nitroprusside (SNP). The following was found: the cells from 18-month-old animals accumulated about twice as much ET-1 per microg DNA under basal (low serum) and stimulated conditions as cells from young rats. All, but PDGF and SNP produced concentration-dependent rise in ET-1 levels, the most effective being 10% FCS, IL-1beta, TNF-alpha, EGF, IGF-1 and LPS. TGF-beta caused the smallest stimulation and PDGF was ineffective or slightly inhibitory at high concentrations. SNP caused concentration-dependent decrease of ET-1 concentrations. ET-1-specific mRNA was identified by RT-PCR in cells incubated with the above factors and its concentration paralleled that of the peptide. This suggests that ET-1 found in the culture media of RAC stems, at least in part, from the synthesis. Increased immunoreactive peptide concentration and mRNA expression with the age of the donor rat and its regulation by several growth factors and cytokines suggest the involvement of ET-1 in chondrocytes' physiology and possibly pathology.

Biology of renal aging in humans

Advancing age is usually accompanied by a decline in glomerular filtration rate and an increased incidence of certain renal and electrolyte disorders. These include an increased susceptibility to acute renal failure, hypo- and hypernatremia, hyperkalemia, and hypertension. This report discusses anatomic and physiological observations related to the aged human kidney and explores the various theories and postulated mechanisms underlying these changes.

A biotinylated perfringolysin O derivative: a new probe for detection of cell surface cholesterol

theta-Toxin is a cholesterol-binding, pore-forming cytolysin of Clostridium perfringens. To detect cell surface cholesterol, we prepared a theta-toxin derivative, BC theta by biotinylation of a protease-nicked theta-toxin, which has the same binding affinity for cholesterol as theta-toxin without cytolytic activity. Human erythrocytes, V79 cells and human umbilical vein endothelial cells (HUVEC), were stained with BC theta coupled with FITC-avidin, and then the cells were analyzed by either flow cytometry or laser confocal microscopy. The fluorescence intensity increased in both intact and briefly fixed cells when treated with BC theta. BC theta-treated V79 cells were stained by neither trypan blue nor propidium iodide, indicating that BC stained just the outer surface of the plasma membrane of vital cells. Treatment of the cells with digitonin, a cholesterol-sequestering reagent, decreased the fluorescence intensity to the background level, indicating that BC theta staining is specific for cholesterol. The fluorescence intensity of erythrocytes pre-permeabilized with a small amount of theta-toxin increased more than ten-fold, suggesting higher cholesterol contents in the inner layer of the plasma membrane. When cells were cultured with cholesterol-depleted medium, the fluorescence intensity stained by BC theta decreased remarkably in V79 cells, but did not change in HUVEC. This indicates that cell surface cholesterol may be provided in different ways with these two cell lines. These results suggest that BC theta can be a useful probe for visualizing cell surface cholesterol and for evaluating the effects of cellular events on the topology and distribution of cholesterol.

Age related decline in cytokine induced nitric oxide synthase activation and apoptosis in cultured endothelial cells: minimal involvement of nitric oxide in the apoptosis

Nitric oxide synthase (NOS) activity was enhanced in human umbilical vein endothelial cells (HUVECs) by the combined stimulation with IFN-gamma plus IL-1beta, TNF-alpha and LPS which was accompanied by cell death. DNA analysis of the NOS induced dead HUVECs showed that internucleosomal DNA fragmentation had occurred, suggesting that apoptosis was taken place. The enhanced NO production seemed to be associated with the death of HUVECs, however, both NG-methyl-L-arginine (L-NMMA) and nitro-L-arginine (N-arg), inhibitors of NOS, recovered the death of HUVECs by only 16%, suggesting that NO production was minimally involved in the cytokine induced apoptosis of HUVECs. Additional results demonstrated that both the induction of NOS activity and apoptosis in HUVECs declined with in vitro aging, i.e. declined with increasing PDLs of HUVECs, which may explain the decreased immunity during inflammation in aged people.