Chemically induced platelet lysis causes vasoconstriction by release of serotonin

Sickle Cell Disease: Metabolomic Profiles of Vaso-Occlusive Crisis in Plasma and Erythrocytes

The metabolomic profile of vaso-occlusive crisis, compared to the basal state of sickle cell disease, has never been reported to our knowledge. Using a standardized targeted metabolomic approach, performed on plasma and erythrocyte fractions, we compared these two states of the disease in the same group of 40 patients. Among the 188 metabolites analyzed, 153 were accurately measured in plasma and 143 in red blood cells. Supervised paired partial least squares discriminant analysis (pPLS-DA) showed good predictive performance for test sets with median area under the receiver operating characteristic (AUROC) curves of 99% and mean p-values of 0.0005 and 0.0002 in plasma and erythrocytes, respectively. A total of 63 metabolites allowed discrimination between the two groups in the plasma, whereas 61 allowed discrimination in the erythrocytes. Overall, this signature points to altered arginine and nitric oxide metabolism, pain pathophysiology, hypoxia and energetic crisis, and membrane remodeling of red blood cells. It also revealed the alteration of metabolite concentrations that had not been previously associated with sickle cell disease. Our results demonstrate that the vaso-occlusive crisis has a specific metabolomic signature, distinct from that observed at steady state, which may be potentially helpful for finding predictive biomarkers for this acute life-threatening episode.

Doxorubicin-induced platelet procoagulant activities: an important clue for chemotherapy-associated thrombosis

Thrombotic risk associated with chemotherapy including doxorubicin (DOX) has been frequently reported; yet, the exact mechanism is not fully understood. Here, we report that DOX can induce procoagulant activity in platelets, an important contributor to thrombus formation. In human platelets, DOX increased phosphatidylserine (PS) exposure and PS-bearing microparticle (MP) generation. Consistently, DOX-treated platelets and generated MPs induced thrombin generation, a representative marker for procoagulant activity. DOX-induced PS exposure appeared to be from intracellular Ca²⁺ increase and ATP depletion, which resulted in the activation of scramblase and inhibition of flippase. Along with this, apoptosis was induced by DOX as determined by the dissipation of mitochondrial membrane potential (Δψ), cytochrome c release, Bax translocation, and caspase-3 activation. A Ca²⁺ chelator ethylene glycol tetraacetic acid, caspase inhibitor Q-VD-OPh, and antioxidants (vitamin C and trolox) can attenuate DOX-induced PS exposure and procoagulant activity significantly, suggesting that Ca²⁺, apoptosis, and reactive oxygen species (ROS) were involved in DOX-enhanced procoagulant activity. Importantly, rat in vivo thrombosis model demonstrated that DOX could manifest prothrombotic effects through the mediation of platelet procoagulant activity, which was accompanied by increased PS exposure and Δψ dissipation in platelets.

Fibrinogen adsorption and platelet lysis characterization of fluorinated surface-modified polyetherurethanes

A polyetherurethane (PU) was modified using fluorinated surface-modifying macromolecules (SMMs). A double radiolabel method was used simultaneously to measure the number of adhered platelets ((51)Cr) and the quantity of adsorbed Fg ((125)I), in a cone-and-plate instrument. The objectives were to determine if adsorbed Fg levels correlated to platelet adhesion on the surfaces, and to assess if any reductions in platelet adhesion for the SMM-treated surfaces resulted from surface-induced platelet lysis, rather than changes directly related to lower platelet activation and attachment on the novel surfaces. Platelet lysis was determined from lactate dehydrogenase (LDH) and unbound (51)Cr released into plasma isolated from whole blood exposed to test materials. The corresponding Fg adsorption, evaluated under the same platelet adhesion conditions, did not account for the reduced platelet adhesion on the treated surfaces. LDH and (51)Cr platelet release were very low and indicated no statistically significant differences between the materials. It was therefore concluded that platelet lysis did not contribute to the reduction in platelet adhesion characteristic observed on the SMM-treated surfaces. More importantly, the work emphasizes that the platelet activation cannot be inferred to by assessing the quantity of fibrinogen as is commonly done in the literature. The finding suggests a much more complex mechanism of action for the SMM surface modifiers. On-going work is investigating other Fg parameters such as protein binding affinity and protein conformational state in order to establish the mechanism by which the fluorinated surface modifiers may be reducing platelet adhesion via intermediary changes in initial protein adsorption.

Inhibitory effect of Andrographis paniculata extract and its active diterpenoids on platelet aggregation

Andrographis paniculata has been widely used for the prevention and treatment of common cold especially in Asia and Scandinavia. The three active diterpenoids from this plant, including aqueous plant extracts, were investigated for the inhibitory effect on platelet aggregation in vitro. The results indicated that andrographolide (AP(1)) and 14-deoxy-11,12-didehydroandrographolide (AP(3)) significantly inhibited thrombin-induced platelet aggregation in a concentration-(1-100 microM) and time-dependent manner while neoandrographolide (AP(4)) had little or no activity. AP(3) exhibited higher antiplatelet activity than AP(1) with IC(50) values ranging from 10 to 50 microM. The inhibitory mechanism of AP(1) and AP(3) on platelet aggregation was also evaluated and the results indicated that the inhibition of extracellular signal-regulated kinase1/2 (ERK1/2) pathway may contribute to antiplatelet activity of these two compounds. In addition, standardized aqueous extracts of A. paniculata containing different amounts of AP(3) inhibited thrombin-induced aggregation to different degrees. The extracts significantly decreased platelet aggregation in a concentration-(10-100 microg/ml) and time-dependent manner. However, the extract with high level of AP(3) (Extract B) (IC(50) values=50-75 microg/ml) showed less inhibitory activity against thrombin than the extract with lower level of AP(3) (Extract A) (IC(50) values=25-50 microg/ml). These results indicate that the standardized A. paniculata extract may contain other antiplatelet compounds rather than AP(1) and AP(3), which contribute to high antiplatelet activity. Therefore, the consumption of A. paniculata products may help to prevent or treat some cardiovascular disorders i.e. thrombosis; however, it should be used with caution by patients with bleeding disorders.

Naphthazarin and methylnaphthazarin cause vascular dysfunction by impairment of endothelium-derived nitric oxide and increased superoxide anion generation

The effects of the naphthoquinone analogue, naphthazarin (Nap), and its derivative, methylnaphthazarin (MetNap), on vascular reactivity were studied using isolated rat aortic rings and human umbilical vein endothelial cells (HUVECs). In this study, we determined vessel tension, nitric oxide (NO) formation, endothelial nitric oxide synthase (eNOS) activity, eNOS protein expression, and superoxide anion (O2*-) generation in an effort to evaluate the effect of Nap and MetNap on the impairment of the NO-mediated pathway. Lower concentrations of Nap (0.01-1 microM) and MetNap (1-10 microM) concentration-dependently enhanced phenylephrine (PE)-induced vasocontraction and abrogated acetylcholine (ACh)-induced vasorelaxation in an endothelium-dependent manner. On HUVECs, both Nap and MetNap concentration-dependently inhibited NO formation induced by A23187, and also partially inhibited nitric oxide synthase (NOS) activity. eNOS protein expression by HUVECs was not affected by treatment with Nap or MetNap, even within 24h. These data suggest that Nap and MetNap might act as inhibitors of nitric oxide synthesis in the endothelium. In addition, Nap and MetNap were also shown to generate O2*- on HUVECs with short-term treatment. We concluded that Nap and MetNap inhibited agonist-induced relaxation and induced vasocontraction in an endothelium-dependent manner, and these effects might have been due to modification of the NO content by inhibition of NOS activity and bioinactivation through O2*- generation.

Mechanisms involved in the early increase of serotonin contraction evoked by endotoxin in rat middle cerebral arteries

The present study investigated the mechanisms involved in the increased 5-hydroxytryptamine (5-HT) vasoconstriction observed in rat middle cerebral arteries exposed in vitro to lipopolysaccharide (LPS, 10 microg x ml-1) for 1-5 h. Functional, immunohistochemical and Western blot analysis and superoxide anion measurements by ethidium fluorescence were performed. LPS exposure increased 5-HT (10 microm) vasoconstriction only during the first 4 h. In contrast to control tissue, indomethacin (10 microm), the COX-2 inhibitor NS 398 (10 microm), the TXA2/PGH2 receptor antagonist SQ 29548 (1 microm) and the TXA2 synthase inhibitor furegrelate (1 microm) reduced 5-HT contraction of LPS-treated arteries from hour one. The iNOS inhibitor aminoguanidine (0.1 mm) increased 5-HT contraction from hour three of LPS incubation. The superoxide anion scavenger superoxide dismutase (SOD, 100 U ml-1) and the H2O2 scavenger catalase (1000 U ml-1), as well as the respective inhibitors of NAD(P)H oxidase and xanthine oxidase, apocynin (0.3 mm) and allopurinol (0.3 mm), reduced 5-HT contraction after LPS incubation. LPS induced an increase in superoxide anion levels that was abolished by PEG-SOD. Subthreshold concentrations of the TXA2 analogue U 46619, xanthine/xanthine oxidase and H2O2 potentiated, whereas those of sodium nitroprusside inhibited, the 5-HT contraction. COX-2 expression was increased at 1 and 5 h of LPS incubation, while that of iNOS, Cu/Zn-SOD and Mn-SOD was only increased after 5 h. All the three vascular layers expressed COX-2 and Cu/Zn-SOD. iNOS expression was detected in the endothelium and adventitia after LPS. In conclusion, increased production of TXA2 from COX-2, superoxide anion and H2O2 enhanced vasoconstriction to 5-HT during the first few hours of LPS exposure; iNOS and SOD expression counteracted that increase at 5 h. These changes can contribute to the disturbance of cerebral blood flow in endotoxic shock.

Induction of vasorelaxation through activation of nitric oxide synthase in endothelial cells by brazilin

The vasorelaxant activity of Caesalpinia sappan L., a traditional Chinese medicine, and its major component brazilin were investigated in isolated rat aorta and human umbilical vein endothelial cells. In isolated rat aorta, C. sappan L. extract and brazilin relaxed phenylephrine-induced vasocontraction and increased cyclic guanosine 3',5'-monophosphate (cGMP) content. Induction of vasorelaxation of brazilin was endothelium-dependent and could be markedly blocked by pretreatment with nitric oxide synthase (NOS) inhibitor, N(G)-nitro-L-arginine methyl ester (L-NAME); N(G)-monomethyl-L-arginine acetate (L-NMMA) and guanylyl cyclase inhibitor, methylene blue; 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) and nitric oxide (NO) scavenger, hemoglobin. The increasing cGMP content induced by brazilin was also blocked by pretreatment with L-NAME, methylene blue, and the removal of extracellular Ca(2+). In human umbilical vein endothelial cells, brazilin dose-dependently induced an increase in NO formation and NOS activity, which were greatly attenuated by either the removal of extracellular Ca(2+) or the chelating of intracellular Ca(2+) chelator, 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA-AM). Moreover, brazilin dose-dependently induced the influx of extracellular Ca(2+) in human umbilical vein endothelial cells. Collectively, these results suggest that brazilin induces vasorelaxation by the increasing intracellular Ca(2+) concentration in endothelial cells of blood vessels and hence activating Ca(2+)/calmodulin-dependent NO synthesis. The NO is released and then transferred into smooth muscle cells to activate guanylyl cyclase and increase cGMP content, resulting in vasorelaxation.

Enhanced menadione cytotoxicity in platelets isolated from streptozotocin-induced diabetic rats

To study whether chemically induced cytotoxicity occurs in diabetic platelets, platelets isolated from rats made hyperglycemic (diabetic) by a prior intravenous administration of streptozotocin were incubated with menadione and the cytotoxicity was assessed by the amount of lactate dehydrogenase (LDH) released from the menadione exposed platelets as a function of time. Platelets isolated from diabetic rats released greater amount of LDH in response to menadione than those from normal rats. Consistent with this finding, induction of menadione cytotoxicity was not dependent on glutathione depletion, but on greater generation of free radicals in diabetic platelets. Greater sensitivity of diabetic platelets to the menadione-induced cytotoxicity was accompanied by release of serotonin from dense granules, suggesting that this mechanism contributes to cardiovascular diseases in diabetic subjects.

Enhancement of platelet aggregation and thrombus formation by arsenic in drinking water: a contributing factor to cardiovascular disease

Arsenic in drinking water is a worldwide health problem that is associated with cardiovascular disease, but the cause is currently unknown. Arsenic effects on platelets, which are important in development of cardiovascular disease, were examined in vitro and in a drinking water study using a rat animal model. Trivalent inorganic arsenic (arsenite) induced in vitro aggregation when platelets were exposed to subthreshold challenge by thrombin and several other agonists in a concentration-dependent manner, with arsenite being the most potent form tested. Arsenite also induced significant increases in serotonin secretion, thromboxane A(2) formation, and adhesion protein expression in platelets. Consistent with the in vitro studies, 4-week ingestion of arsenite-contaminated drinking water resulted in enhanced arterial thrombosis. Human platelets showed similar responses, suggesting that the effects seen in animal experiments are applicable to humans. These results will provide new insights into the mechanism of arsenic-induced cardiovascular disease. They will also allow regulatory agencies to estimate risk from arsenic-induced cardiovascular disease and to determine if drinking water regulatory levels based on human cancer studies will protect against noncancer effects associated with cardiovascular disease.

Menadione induces endothelial dysfunction mediated by oxidative stress and arylation

Our previous studies showed that menadione causes endothelial dysfunction which results in decreased relaxation and increased contraction of blood vessels. This investigation examined the role of two possible mechanisms (oxidative stress and arylation) in menadione-induced endothelial dysfunction. Menadione increased superoxide anion generation in aortic rings in a dose-dependent manner. Superoxide dismutase (SOD), reversed the inhibitory effects of menadione on vascular relaxation. The relaxation induced by the NO donor, sodium nitroprusside, was inhibited by menadione pretreatment in a dose-dependent manner. Endothelial nitric oxide synthase activity (eNOS) was suppressed by menadione. Menadione resulted in a dose-dependent reduction of cGMP levels accumulated by acetylcholine. This reduction of cGMP levels was blocked by SOD treatment, suggesting that superoxide anion generated by menadione could play a role in the inhibition of the nitric oxide pathway. Evidence supporting a possible role for arylation in impaired vascular relaxation was suggested by the observation that benzoquinone, which does not induce oxidative stress in aortic rings, inhibited acetylcholine-induced vascular relaxation to the same extent as menadione. Collectively, these results suggest that menadione can cause endothelial dysfunction in blood vessels by the inhibition of the nitric oxide pathway via superoxide anion generation and that arylation activity may also be another important mechanism.

Age-related responses of the microcirculation to ischemia-reperfusion and inflammation

Aging is a major risk factor for a variety of ischemic disorders including ischemic heart disease and stroke. Intense research over the past decade into ischemia-reperfusion (I/R) injury has implicated a general mechanism whereby reactive oxygen species produced at the onset of reperfusion overwhelm endogenous antioxidants, resulting in a cascade of events including mast cell degranulation, recruitment of neutrophils to the endothelial wall, arteriolar constriction that limits tissue perfusion, and increased vascular permeability that leads to inflammation and edema. Much of our knowledge regarding I/R injury comes from animal models; however, despite the fact that I/R disproportionately affects older individuals, young animals are usually chosen in models of I/R injury due to their greater availability, lower cost, and fewer health problems. Results obtained from young animals demonstrate a central role for both neutrophils and mast cells in I/R-induced increases in microvascular permeability and arteriolar constriction; however, it is not clear that a role for neutrophils is extended to older animals. A growing body of evidence indicates that neutrophils isolated from elderly individuals exhibit attenuated chemotaxis, oxidant release, and phagocytosis, and it has been suggested that these deficiencies are related to an age-associated increase in glucocorticoid production and oxidative stress. Therefore, neutrophils may have a limited capacity to influence microcirculatory tissue in the elderly compared to in the young. In support of this hypothesis, I/R-induced increases in microvascular permeability and decreases in vascular perfusion have been found to occur in older rats despite the absence of a significant increase in leukocyte-endothelial cell adhesion. Furthermore, elimination of circulating neutrophils attenuates I/R-induced mesenteric permeability only in young rats. Therefore, it appears that neutrophil-independent mechanisms of inflammation may be responsible for much of the microvascular dysfunction initiated by I/R in older animals.

Intracortical hemorrhage injury in rats : relationship between blood fractions and brain cell death

BACKGROUND AND PURPOSE

Intracerebral hemorrhage is associated with stroke and head trauma. The purposes of this study were to investigate the effect of intracortical injections of autologous whole blood and blood components on inflammatory cell infiltration and brain cell death and to determine if nonhemorrhagic lesions differ in these respects.

METHODS

Eighty-seven adult rats were subjected to intracortical injections of autologous whole blood or allogeneic plasma, erythrocytes, leukocytes, "activated" leukocytes, and serum. Injections of saline or mineral oil were controls. Blood injections were compared with cortical freeze injury and pial devascularization. Rats were perfusion-fixed 48 hours after injection or lesioning. Eosinophilic neurons, TUNEL-positive cells, brain damage area, infiltrating neutrophils, and CD8a-immunoreactive lymphocytes were quantified.

RESULTS

Damage area, dying cells, and inflammatory infiltrate were significantly greater after autologous whole blood, leukocyte, and "activated" leukocyte injections than injection of other fractions.

CONCLUSIONS

These results suggest that extravasated whole blood causes a greater degree of cortical cell death and inflammation than ischemic lesions of similar size. Leukocytes "activated" by systemic illness might exacerbate the injury. Secondary hemorrhagic phenomena suggest that the harmful effect is directed toward both brain cells and the vasculature. Further studies are required to delineate the mechanism(s).

Menadione-induced vascular endothelial dysfunction and its possible significance

Although several studies have shown that treatment with menadione leads to endothelial cell cytotoxicity, investigations of menadione's effects on blood vessels are limited. Our previous studies have shown that menadione can indirectly induce alterations in vasomotor tone through platelet cytotoxicity. To determine if menadione affects vascular function, we investigated the effect of menadione on blood vessels using the isolated rat aortic rings in vitro organ bath system. Treatment with menadione directly resulted in contraction of aortic rings with endothelium but did not cause any effect on aortic rings without endothelium. Menadione irreversibly inhibited the acetylcholine- and histamine-induced relaxation of aortic rings with endothelium in a time- and concentration-dependent manner. Menadione treatment potentiated phenylephrine- and serotonin-induced vasoconstriction in aortic rings with endothelium. These in vitro results were observed at concentrations of menadione that are highly relevant to human therapeutics with menadione. When menadione was administrated intravenously to rats, blood pressure increased significantly in a concentration-dependent manner. Furthermore, menadione infusion suppressed the blood pressure reduction induced by acetylcholine. By demonstrating that menadione caused in vitro endothelial dysfunction (i.e., decreased relaxation and increased vasoconstriction in the organ bath experiments) and confirming that these results were consistent with in vivo observations, we have provided evidence suggesting that a quinone such as menadione can alter vasomotor tone through endothelial dysfunction. Such dysfunction could possibly contribute to vascular diseases.

The biological significance of non-enzymatic reaction of menadione with plasma thiols: enhancement of menadione-induced cytotoxicity to platelets by the presence of blood plasma

To test the hypothesis that the non-enzymatic reaction of quinones with thiols in plasma can generate reactive oxygens (ROS), thereby leading to potentiated cellular toxicity, we have studied the effect of a representative quinone compound, menadione, on plasma isolated from rats. The experimental results are as follows: (1) menadione generated ROS via non-enzymatic reaction with protein thiols in plasma; (2) the presence of plasma increased menadione-induced cytotoxicity to platelets; (3) pretreatment of plasma with a thiol-depleting agent significantly suppressed menadione-induced ROS and cytotoxicity. These results suggest that the non-enzymatic reaction of menadione with plasma thiols could be an important process in quinone-induced cellular toxicity.