Signalling pathways involved in p47phox -dependent reactive oxygen species in platelets of endotoxemic rats

Thrombocytopenia during sepsis is associated with a less favourable clinical outcome. Overproduction of reactive oxygen species (ROS) by different cell types contributes to sepsis. Platelets generate ROS, but the upstream pathways of NADPH oxidase activation are not completely understood. Here, we designed experiments in washed platelets from lipopolysaccharide (LPS)-treated rats to investigate the p47^phox activation and ROS generation, and its modulation by c-Src family kinase (c-Src), phosphoinositide 3-kinase (PI3K), protein kinase C (PKC) and protein kinase G (PKG). Rats were injected intraperitoneally with LPS (1 mg/kg), and at 48 hours thereafter, arterial blood was collected and washed platelets were obtained. Washed platelets were pre-incubated with different inhibitors and subsequently activated or not with ADP. Flow cytometry, Western blotting and ELISA were performed. We found that LPS significantly increased the p47^phox phosphorylation and ROS generation compared with the control group (P < 0.05). The enhanced ROS production in the LPS group was unaffected by the non-selective SFKs inhibitor PP2, the PI3K inhibitor wortmannin or the Akt inhibitor PPI-1. The cyclic GMP levels were 115% higher in activated platelets of LPS compared with the saline group (P < 0.05). Moreover, in the LPS group, the sGC inhibitor ODQ, the PKG inhibitor Rp-8-Br and the PKC inhibitor GF109203X abrogated the increased p47^phox phosphorylation and reduced the ROS levels. In conclusion, selective inhibitors of cGMP-PKG and PKC-p47^phox pathways that regulate ROS generation by LPS in platelets may help control the redox balance in sepsis improving the survival of patients.

Discovery of phenylsulfonylfuroxan derivatives as gamma globin inducers by histone acetylation

N-oxide derivatives 5(a-b), 8(a-b), and 11(a-c) were designed, synthesized and evaluated in vitro and in vivo as potential drugs that are able to ameliorate sickle cell disease (SCD) symptoms. All of the compounds demonstrated the capacity to releasing nitric oxide at different levels ranging from 0.8 to 30.1%, in vivo analgesic activity and ability to reduce TNF-α levels in the supernatants of monocyte cultures. The most active compound (8b) protected 50.1% against acetic acid-induced abdominal constrictions, while dipyrone, which was used as a control only protected 35%. Compounds 8a and 8b inhibited ADP-induced platelet aggregation by 84% and 76.1%, respectively. Both compounds increased γ-globin in K562 cells at 100 μM. The mechanisms involved in the γ-globin increase are related to the acetylation of histones H3 and H4 that is induced by these compounds. In vitro, the most promising compound (8b) was not cytotoxic, mutagenic and genotoxic.

Lipopolysaccharide potentiates platelet responses via toll-like receptor 4-stimulated Akt-Erk-PLA2 signalling

Lipopolysaccharide (LPS) from the cell envelope of Gram-negative bacteria is a principal cause of the symptoms of sepsis. LPS has been reported to modulate the function of platelets although the underlying mechanisms of LPS action in these cells remain unclear. Platelets express the Toll-like receptor 4 (TLR4) which serves as a receptor for LPS, although the potential role of TLR4 and associated cell signalling in controlling platelet responses to LPS has not been extensively explored. In this study, we therefore investigated the actions of LPS prepared from different strains of Escherichia coli on platelet function, the underlying signalling mechanisms, and the potential role of TLR4 in orchestrating these. We report that LPS increased the aggregation of washed platelets stimulated by thromboxane (U46619) or GPVI collagen receptor agonists, effects that were prevented by a TLR4 antagonist. Associated with this, LPS enhanced fibrinogen binding, P-selectin exposure and reactive oxygen species (ROS) release. Increase of ROS was found to be important for the actions of LPS on platelets, since these were inhibited in the presence of superoxide dismutase or catalase. The effects of LPS were associated with phosphorylation of Akt, ERK1/2 and PLA2 in stimulated platelets, and inhibitors of PI3-kinase, Akt and ERK1/2 reduced significantly LPS enhanced platelet function and associated ROS production. Furthermore, inhibition of platelet cyclooxygenase or the thromboxane receptor, revealed an important role for thromboxane A2. We therefore conclude that LPS increases human platelet activation through a TLR4-PI3K-Akt-ERK1/2-PLA2 -dependent pathway that is dependent on ROS and TXA2 formation.

Synthesis, antiplatelet and antithrombotic activities of resveratrol derivatives with NO-donor properties

Resveratrol (RVT) is a stilbene with a protective effect on the cardiovascular system; however, drawbacks including low bioavailability and fast metabolism limit its efficacy. In this work we described new resveratrol derivatives with nitric oxide (NO) release properties, ability to inhibit platelet aggregation and in vivo antithrombotic effect. Compounds (4a-f) were able to release NO in vitro, at levels ranging from 24.1% to 27.4%. All compounds (2a-f and 4a-f) have exhibited platelet aggregation inhibition using as agonists ADP, collagen and arachidonic acid. The most active compound (4f) showed reduced bleeding time compared to acetylsalicylic acid (ASA) and protected up to 80% against in vivo thromboembolic events. These findings suggest that hybrid resveratrol-furoxan (4f) is a novel lead compound able to prevent platelet aggregation and thromboembolic events.

Cross-talking between lymphocytes and platelets and its regulation by nitric oxide and peroxynitrite in physiological condition and endotoxemia

AIMS

Cross-talk between platelets and lymphocytes may play a role in different pathological conditions like sepsis. This study aimed to investigate the effect of lymphocytes on platelet aggregation in lipopolysaccharide (LPS)-stimulated and non-stimulated cells.

MAIN METHODS

Lymphocytes and platelet-rich plasma (PRP) were obtained from rat arterial blood. Platelets (1.2×10⁸platelets/ml) were incubated with lymphocytes (0.8×10⁶cells/ml) in the presence or not of LPS (100μg/ml), after which ADP (5μM)-induced platelet aggregation was carried out.

KEY FINDINGS

Lymphocytes inhibited by 51% the platelet aggregation, which was significantly prevented by the non-selective NO inhibitor l-NAME (300μM) or the selective iNOS inhibitor 1400W (100μM), as well as by the soluble guanylyl cyclase (sGC) inhibitor ODQ (10μM). The platelet inhibition by lymphocytes was accompanied by 2-fold increase of intraplatelet cGMP levels. Next, lymphocytes and platelets were co-incubated with LPS for 6h. In LPS-treated cells, lymphocytes produced a larger inhibition of platelet aggregation (62%), despite the same elevation of cGMP levels (2.2-fold increase). This inhibitory effect was prevented by l-NAME and 1400W, but rather unaffected by ODQ. The peroxynitrite (ONOO^-) scavenger -(-)epigallocatechin gallate (ECG, 100μM) abolished the inhibition by lymphocytes on platelet aggregation in LPS-treated cells, but not in non-treated cells.

SIGNIFICANCE

Our results show that lymphocytes act to inhibit platelet aggregation via iNOS-derived NO release and cGMP generation. In presence of LPS, ONOO^- production accounts for the platelet inhibition.

PKC and AKT Modulate cGMP/PKG Signaling Pathway on Platelet Aggregation in Experimental Sepsis

Sepsis severity has been positively correlated with platelet dysfunction, which may be due to elevations in nitric oxide (NO) and cGMP levels. Protein kinase C, Src kinases, PI3K and AKT modulate platelet activity in physiological conditions, but no studies evaluated the role of these enzymes in platelet aggregation in sepsis. In the present study we tested the hypothesis that in sepsis these enzymes positively modulate upstream the NO-cGMP pathway resulting in platelet inhibition. Rats were injected with lipopolysaccharide (LPS, 1 mg/kg, i.p.) and blood was collected after 6 h. Platelet aggregation was induced by ADP (10 μM). Western blotting assays were carried out to analyze c-Src and AKT activation in platelets. Intraplatelet cGMP levels were determined by enzyme immunoassay kit. Phosphorylation of c-SRC at Tyr416 was the same magnitude in platelets of control and LPS group. Incubation of the non-selective Src inhibitor PP2 (10 μM) had no effect on platelet aggregation of LPS-treated rats. LPS increased intraplatelet cGMP levels by 5-fold compared with control group, which was accompanied by 76% of reduction in ADP-induced platelet aggregation. The guanylyl cyclase inhibitor ODQ (25 μM) and the PKG inhibitor Rp-8-Br-PET-cGMPS (25 μM) fully reversed the inhibitory effect of LPS on platelet aggregation. Likewise, the PKC inhibitor GF109203X (10 μM) reversed the inhibition by LPS of platelet aggregation and decreased cGMP levels in platelets. AKT phosphorylation at Thr308 was significantly higher in platelets of LPS compared with control group, which was not reduced by PI3K inhibition. The AKT inhibitor API-1 (20 μM) significantly increased aggregation and reduced cGMP levels in platelets of LPS group. However, the PI3K inhibitor wortmannin and LY29004 had no effect on platelet aggregation of LPS-treated rats. Therefore, inhibition of ADP-induced platelet aggregation after LPS injection is mediated by cGMP/PKG-dependent mechanisms, and PKC and AKT act upstream upregulating this pathway.

Activation of haem-oxidized soluble guanylyl cyclase with BAY 60-2770 in human platelets lead to overstimulation of the cyclic GMP signaling pathway

BACKGROUND AND AIMS

Nitric oxide-independent soluble guanylyl cyclase (sGC) activators reactivate the haem-oxidized enzyme in vascular diseases. This study was undertaken to investigate the anti-platelet mechanisms of the haem-independent sGC activator BAY 60-2770 in human washed platelets. The hypothesis that sGC oxidation potentiates the anti-platelet activities of BAY 60-2770 has been tested.

METHODS

Human washed platelet aggregation and adhesion assays, as well as flow cytometry for α(IIb)β(3) integrin activation and Western blot for α1 and β1 sGC subunits were performed. Intracellular calcium levels were monitored in platelets loaded with a fluorogenic calcium-binding dye (FluoForte).

RESULTS

BAY 60-2770 (0.001-10 µM) produced significant inhibition of collagen (2 µg/ml)- and thrombin (0.1 U/ml)-induced platelet aggregation that was markedly potentiated by the sGC inhibitor ODQ (10 µM). In fibrinogen-coated plates, BAY 60-2770 significantly inhibited platelet adhesion, an effect potentiated by ODQ. BAY 60-2770 increased the cGMP levels and reduced the intracellular Ca(2+) levels, both of which were potentiated by ODQ. The cell-permeable cGMP analogue 8-Br-cGMP (100 µM) inhibited platelet aggregation and Ca(2+) levels in an ODQ-insensitive manner. The cAMP levels remained unchanged by BAY 60-2770. Collagen- and thrombin-induced α(IIb)β(3) activation was markedly inhibited by BAY 60-2770 that was further inhibited by ODQ. The effects of sodium nitroprusside (3 µM) were all prevented by ODQ. Incubation with ODQ (10 µM) significantly reduced the protein levels of α1 and β1 sGC subunits, which were prevented by BAY 60-2770.

CONCLUSION

The inhibitory effects of BAY 60-2770 on aggregation, adhesion, intracellular Ca(2+) levels and α(IIb)β(3) activation are all potentiated in haem-oxidizing conditions. BAY 60-2770 prevents ODQ-induced decrease in sGC protein levels. BAY 60-2770 could be of therapeutic interest in cardiovascular diseases associated with thrombotic complications.

Platelet hyperaggregability in high-fat fed rats: a role for intraplatelet reactive-oxygen species production

Background

Adiposity greatly increases the risk of atherothrombotic events, a pathological condition where a chronic state of oxidative stress is reported to play a major role. This study aimed to investigate the involvement of (NO)-soluble guanylyl cyclase (sGC) signaling pathway in the platelet dysfunction from high fat-fed (HFF) rats.

Methods

Male Wistar rats were fed for 10 weeks with standard chow (SCD) or high-fat diet (HFD). ADP (10 μM)- and thrombin (100 mU/ml)-induced washed platelet aggregation were evaluated. Measurement of intracellular levels of ROS levels was carried out using flow cytometry. Cyclic GMP levels were evaluated using ELISA kits.

Results

High-fat fed rats exhibited significant increases in body weight, epididymal fat, fasting glucose levels and glucose intolerance compared with SCD group. Platelet aggregation induced by ADP (n = 8) and thrombin from HFD rats (n = 8) were significantly greater (P < 0.05) compared with SCD group. Platelet activation with ADP increased by 54% the intraplatelet ROS production in HFD group, as measured by flow cytometry (n = 6). N-acetylcysteine (NAC; 1 mM) and PEG-catalase (1000 U/ml) fully prevented the increased ROS production and platelet hyperaggregability in HFD group. The NO donors sodium nitroprusside (SNP; 10 μM) and SNAP (10 μM), as well as the NO-independent soluble guanylyl cyclase stimulator BAY 41-2272 (10 μM) inhibited the platelet aggregation in HFD group with lower efficacy (P < 0.05) compared with SCD group. The cGMP levels in response to these agents were also markedly lower in HFD group (P < 0.05). The prostacyclin analogue iloprost (1 μM) reduced platelet aggregation in HFD and SCD rats in a similar fashion (n = 4).

Conclusions

Metabolic abnormalities as consequence of HFD cause platelet hyperaggregability involving enhanced intraplatelet ROS production and decreased NO bioavailability that appear to be accompanied by potential defects in the prosthetic haem group of soluble guanylyl cyclase.

Reactive oxygen and nitrogen species modulate the ex-vivo effects of LPS on platelet adhesion to fibrinogen

AIMS

Excessive production of nitric oxide (NO) and reactive oxygen species (ROS) in sepsis modulates different cell functions. Since the sepsis severity is associated with the degree of platelet activation, we decided to investigate the role of systemic generation of NO and ROS in modulating the platelet adhesion of lipopolysaccharide (LPS)-treated rats.

MAIN METHODS

Platelet adhesion was evaluated using fibrinogen-coated 96-well microtiter plates. Cyclic GMP levels were measured using enzyme immunoassay kit.

KEY FINDINGS

Treatment of rats with LPS significantly increased spontaneous platelet adhesion, but reduced the thrombin-activated platelet adhesion when compared with control rats. Chronic treatment of rats with the NO synthase inhibitor L-NAME (20 mg/rat/day, 7 days) prior to LPS injection normalized the increased adhesion in non-activated platelets, but failed to affect the adhesion in thrombin-activated platelets. The cGMP levels were modified neither in non-activated nor in thrombin-activated platelets of LPS-treated rats when compared with control rats. The incubation of non-activated platelets with the O2- scavenger PEG-SOD reversed the stimulatory effect of LPS on spontaneous adhesion, but had no effect in stimulated-platelet adhesion of non-treated or LPS-treated groups. Moreover, pretreatment of rats with the antioxidant N-acetylcysteine (NAC; 150 mg/kg) prevented the increase of non-activated platelet adhesion, and significantly reduced the inhibitory effect of LPS on thrombin-stimulated adhesion.

SIGNIFICANCE

Our findings suggest that in LPS-treated rats, NO plays an important modulatory role only in non-stimulated platelet adhesion through cGMP-independent mechanisms, while ROS, directly or by affecting the redox state of the animals, modulates both non-activated and thrombin-activated platelet adhesion.

Lipopolysaccharide treatment reduces rat platelet aggregation independent of intracellular reactive-oxygen species generation

High production of reactive-oxygen species (ROS) by blood cells is involved in damage of the vascular endothelium and multiple organ dysfunction in sepsis. However, little is known about the intraplatelet ROS production in sepsis and its consequences on platelet reactivity. In this study, we evaluated whether the treatment of rats with lipopolysaccharide (LPS) affects platelet aggregation through intraplatelet ROS generation. Rats were injected with LPS (1 mg/kg, i.p.), and at 2 to 72 h thereafter, adenosine diphosphate (ADP) (3-10 µM) induced platelet aggregation was evaluated. Production of ROS in platelets was measured by flow cytometry using 2',7'-dichlorofluorescein diacetate (DCFH-DA). Treatment of rats with LPS time-dependently inhibited ADP-induced platelet aggregation within 72 h. The inhibitory effect of LPS on platelet aggregation was further increased when the platelets were incubated with polyethylene glycol-superoxide dismutase (PEG-SOD; 30 U/mL), polyethylene glycol-catalase (PEG-CAT; 1000 U/mL) or the NADPH oxidase inhibitor diphenyleneiodonium (DPI; 10 µM). The ROS production in non-stimulated platelets did not differ between control and LPS-treated rats. However, in ADP-activated platelets, generation of ROS was increased by 3.0- and 7.0-fold, as evaluated at 8 and 48 h after LPS injection, respectively. This increased ROS production was significantly reduced when platelets were incubated in vitro with DPI, PEG-SOD or PEG-CAT. In contrast, treatment of rats with N-acetylcysteine (150 mg/kg, i.p.) significantly reduced the inhibitory effect of LPS on platelet aggregation, and prevented the increased ROS production by in vivo LPS. Our results indicate that the increased intraplatelet ROS production does not contribute to the inhibitory effect of LPS on platelet aggregation; however, the maintenance of redox balance in LPS-treated rats is fundamental to restore the normal platelet response in these animals.

Mechanisms underlying the inhibitory effects of lipopolysaccharide on human platelet adhesion

Alterations in platelet aggregation in septic conditions are well established. However, little is known about the effects of lipopolysaccharide (LPS) on platelet adhesion. We have therefore investigated the effects of LPS in human platelet adhesion, using an in vitro model of platelet adhesion to fibrinogen-coated wells. Microtiter plates were coated with human fibrinogen, after which washed platelets (6 x 10(8) platelets/ml) were allowed to adhere. Adherent platelets were quantified through measurement of acid phosphatase activity. Calcium mobilization in Fura2-AM-loaded platelets was monitored with a spectrofluorimeter. Platelet flow cytometry in thrombin-stimulated platelets was performed using monoclonal mouse anti-platelet GPIIb/IIIa antibody (PAC-1). Prior incubation of washed platelets with LPS (0.01-300 microg/ml) for 5 to 60 min concentration- and time-dependently inhibited non-activated platelet adhesion. In thrombin-activated (50 mU/ml) platelets, LPS inhibited the adhesion to a significantly lesser extent than non-activated platelets. Cyclohexamide, superoxide dismutase polyethylene glycol (PEG-SOD) or catalase polyethylene glycol did not affect the LPS responses. No alterations in cyclic GMP levels were seen after platelet incubation with LPS, except with the highest concentration employed (300 microg/ml) where an increase of 36% (P < 0.05) was observed. Thrombin increased by 7.5-fold the internal Ca(2+) platelet levels, an effect markedly inhibited by LPS. Thrombin induced concentration-dependent platelet GPIIb/IIIa activation, but LPS failed to affect the activation state of this membrane glycoprotein. In conclusion, LPS inhibits human platelet adhesion to fibrinogen by mechanisms involving blockade of external Ca(2+), independently of cGMP generation and activation of GPIIb/IIIa complex.

Inhibitory effects of staphylococcal enterotoxin type B on human platelet adhesion in vitro

Septic shock was formerly recognized as a consequence of Gram-negative bacteraemia, but at present the incidence of Gram-positive sepsis seems to be more relevant, contributing for more than 50% of cases. Staphylococcal aureus can induce toxic shock in humans through the production of potent toxins termed Staphylococcal enterotoxins, from which Staphylococcal enterotoxin type B (SEB) is one of most studied. Platelets are reported to participate in pathogenesis of severe sepsis, but the exact role of platelets in this event is poorly investigated, particularly that caused by Gram-positive bacteria. Therefore, we have used the model of platelet adhesion to fibrinogen-coated plates to investigate the actions of SEB on human platelets. Ninety-six-well microtiter plates were coated with human fibrinogen (50 microg/mL), and human washed platelet suspension (6 x 10(6) platelets) was added to each well. Adherent platelets were quantified through measurement of acid phosphatase activity. Staphylococcal enterotoxin B (0.0001-30 microg/mL, incubated for 5 to 60 min) time- and dose-dependently inhibited platelet adhesion. This response was modified neither by the protein synthesis inhibitor puromycin (0.01 and 0.1 mM) nor by the superoxide scavengers superoxide dismutase (SOD, 100 units/mL) and polyethylene glycol-SOD (30 U/mL). The peroxide hydrogen (H(2)O(2)) scavenger catalase polyethylene glycol (1000 U/mL) significantly attenuated the platelet adhesion inhibition by SEB. The cAMP and cGMP levels were not changed by SEB (0.0001-30 microg/mL, 60 min). Our findings suggest that H(2)O(2) at least partly contributes to the inhibitory responses of human platelet adhesion by SEB.

Cyclic GMP-independent mechanisms contribute to the inhibition of platelet adhesion by nitric oxide donor: a role for alpha-actinin nitration

The nitric oxide-mediated actions are mostly due to cyclic GMP (cGMP) formation, but cGMP-independent mechanisms, such as tyrosine nitration, have been suggested as potential signaling pathways modulating the NO-induced responses. However, the mechanisms that lead to tyrosine nitration in platelets are poorly studied, and the protein targets of nitration have not been identified in these cells. Therefore, we have used the model of platelet adhesion to fibrinogen-coated plates to investigate the cGMP-independent mechanisms of the NO-donor sodium nitroprusside (SNP) that leads to inhibition of platelet adhesion. SNP concentration-dependently inhibited platelet adhesion, as observed at 15-min and 60-min adhesion. Additionally, SNP markedly increased the cGMP levels, and the soluble guanylate inhibitor ODQ nearly abolished the SNP-mediated cGMP elevations in all experimental conditions used. Nevertheless, ODQ failed to affect the adhesion inhibition obtained with 1.0 mM SNP at 15 min. On the other hand, superoxide dismutase or peroxynitrite (ONOO(-)) scavenger epigallocatechin gallate significantly reversed the inhibition of platelet adhesion by SNP (1 mM, 15 min). Western blot analysis in SNP (1 mM, 15 min)-treated platelets showed a single tyrosine-nitrated protein with an apparent mass of approximately 105 kDa. Nanospray LC-MS/MS identified the human alpha-actinin 1 cytoskeletal isoform (P12814) as the protein contained in the nitrated SDS gel band. Thus, tyrosine nitration of alpha-actinin, through ONOO(-) formation, may be a key modulatory mechanism to control platelet adhesion.

The Plasma and Tissue Kininogen-kallikrein-kinin System: Role in the Cardiovascular System

Bradykinin and Lys-bradykinin are potent peptide mediators implicated in several physiopathological effects in mammals. They act through activation of G-protein-coupled constitutive B(2) or inducible kinin B(1) receptors linked to signaling pathways involving increased intracellular Ca(++) concentrations and/or release of mediators including arachidonic acid metabolites, NO and EDHF. In the cardiovascular system, the kallikrein-kinin system exerts a fine control of vascular smooth muscle tone and arterial blood pressure, and plays a significant cardioprotective effect. This has been lately confirmed in experimental studies employing transgenic mice overexpressing human tissue kallikrein and animals with knockout of kinin B(1) and B(2) receptor gene. Disturbances in this system are associated with arterial hypertension, myocardial ischaemia and other clinical complications. Inhibitors of kininase II (angiotensin-converting enzyme) have been prescribed successfully to patients with cardiovascular diseases, but there is still a great interest in developing drugs or pharmacological strategies that augment the activity of kininogen-kallikrein-kinin system in pathological conditions. Delivery of adenovirus vector containing the human tissue kallikrein gene (gene kallikrein therapy) has emerged as a great potential to satisfy these conditions. This review provides a summary of plasma and tissue kallikrein-kinin system, focusing on the pharmacological properties, kinin receptors and drugs reported to interfere with their actions. The modulatory effects of the kallikrein-kinin system on cardiovascular system, particularly in regulating smooth muscle tone and arterial blood pressure and in preventing myocardium ischaemia have also been explored in the review.

Role of cyclic GMP on inhibition by nitric oxide donors of human eosinophil chemotaxis in vitro

1. This study was designed to investigate the effects of the nitric oxide (NO) donors sodium nitroprusside (SNP), 3-morpholinosydnonimine (SIN-1) and S-nitroso-N-acetylpenicillamine (SNAP) on N-formyl-L-methionyl-L-leucyl-phenylalanine (fMLP, 1 x 10(-7) M)-induced human eosinophil chemotaxis, cyclic guanosine-3',5'-monophosphate (cGMP) levels, protein nitration and cytotoxicity. 2. Human eosinophils were exposed to SNP, SIN-1 and SNAP (0.001-1.0 mM) for either short (10 min) or prolonged (90 min) time periods. Exposition of eosinophils with these NO donors significantly inhibited the eosinophil chemotaxis irrespective of whether cells were exposed to these agents for 10 or 90 min. No marked differences were detected among them regarding the profile of chemotaxis inhibition. 3. Exposition of eosinophils to SNP, SIN-1 and SNAP (0.001-1.0 mM) markedly elevated the cGMP levels above basal levels, but the 90-min exposition resulted in significantly higher levels compared with the 10-min protocols (5.3+/-0.6 and 2.6+/-0.2 nM 1.5 x 10(6) cells(-1), respectively). The cGMP levels achieved with SNAP were greater than SNP and SIN-1. 4. The NO donors did not induce cell toxicity in any experimental condition used. Additionally, eosinophils exposed to SNP, SIN-1 and SNAP (1.0 mM each) either for 10 or 90 min did not show any tyrosine nitration in conditions where a strong nitration of bovine serum albumin was observed. 5. Our findings show that inhibitory effects of fMLP-induced human eosinophil chemotaxis by NO donors at short or prolonged exposition time were accompanied by significant elevations of cGMP levels. However, additional elevations of cGMP levels do not change the functional profile (chemotaxis inhibition) of stimulated eosinophils.

Inhibition of heparin synthesis by methotrexate in rats in vivo

The content and synthesis of heparin and mast cell-dependent skin oedema (as an indirect evaluation of histamine and serotonin content) were investigated in the rat skin after chronic treatment with compound 48/80, a mast cell degranulating substance. The effect of methotrexate, a folic acid analogue that interrupts the synthesis of DNA and RNA, on heparin synthesis and amine storage also was evaluated in rat skin. The heparin content at 6 and 240 hr after treatment with compound 48/80 was reduced markedly (86 and 64%, respectively). At 6 hr, heparin synthesis increased 3.1-fold compared with control animals; maximal synthesis occurred at 24 hr post-treatment (12.8-fold increase), decaying at 240 hr (2.4-fold increase). The dermatan sulfate content and synthesis were not affected by treatment with compound 48/80. Autoradiographic analysis revealed that methotrexate (2.5mg/kg for 3 consecutive days) abolished heparin synthesis at 6, 24, and 72 hr after compound 48/80 treatment, without affecting dermatan sulfate synthesis. The oedema induced by intradermal injection of compound 48/80 (1 microg/site) into the rat skin was decreased significantly at 6 hr after chronic treatment with this compound, but was restored completely 72 hr post-treatment. This pattern of oedematogenic response was also observed in the methotrexate-treated rats. In conclusion, our results show that methotrexate suppresses heparin synthesis without affecting the synthesis of either dermatan sulfate or the co-stored amines histamine/serotonin (as evaluated by measuring the mast cell-dependent oedema), suggesting that the enzyme system involved in heparin synthesis is inducible.

Diabetes-associated nitration of tyrosine and inactivation of succinyl-CoA:3-oxoacid CoA-transferase

High levels of reactive species of nitrogen and oxygen in diabetes may cause modifications of proteins. Recently, an increase in protein tyrosine nitration was found in several diabetic tissues. To understand whether protein tyrosine nitration is the cause or the result of the associated diabetic complications, it is essential to identify specific proteins vulnerable to nitration with in vivo models of diabetes. In the present study, we have demonstrated that succinyl-CoA:3-oxoacid CoA-transferase (SCOT; EC 2.8.3.5) is susceptible to tyrosine nitration in hearts from streptozotocin-treated rats. After 4 and 8 wk of streptozotocin administration and diabetes progression, SCOT from rat hearts had a 24% and 39% decrease in catalytic activity, respectively. The decrease in SCOT catalytic activity is accompanied by an accumulation of nitrotyrosine in SCOT protein. SCOT is a mitochondrial matrix protein responsible for ketone body utilization. Ketone bodies provide an alternative source of energy during periods of glucose deficiency. Because diabetes results in profound derangements in myocardial substrate utilization, we suggest that SCOT tyrosine nitration is a contributing factor to this impairment in the diabetic heart.

Nitration of succinyl-CoA:3-oxoacid CoA-transferase in rats after endotoxin administration

The tyrosine nitration of proteins has been observed in diverse inflammatory conditions and has been linked to the presence of reactive nitrogen species. From many in vitro experiments, it is apparent that tyrosine nitration may alter the function of proteins. A limited number of experiments under in vivo conditions also demonstrate that protein nitration is associated with altered cellular processes. To understand the association of protein nitration with the pathogenic mechanism of the disease, it is essential to identify specific protein targets of nitration with in vivo or intact tissue models. Using anti-nitrotyrosine antibodies, we demonstrated the accumulation of nitrotyrosine in a 52-kDa protein in rat kidney after lipopolysaccharide treatment. The 52-kDa protein was purified and identified with partial sequence as succinyl-CoA:3-oxoacid CoA-transferase (SCOT; EC ). Western blot analysis revealed that the nitration of this mitochondrial enzyme increased in the kidneys and hearts of lipopolysaccharide-treated rats, whereas its catalytic activity decreased. These data suggest that tyrosine nitration may be a mechanism for the inhibition of SCOT activity in inflammatory conditions. SCOT is a key enzyme for ketone body utilization. Thus, tyrosine nitration of the enzyme with sepsis or inflammation may explain the altered metabolism of ketone bodies present in these disorders.

Platelets induce human umbilical vein endothelial cell proliferation through P-selectin

We studied whether platelets could participate in the endothelial cell monolayer regeneration in the case of a vessel damage. Incorporation of [3H]-thymidine into the DNA of human umbilical vein endothelial cells (HUVECs) was measured after 48 h of co-incubation with platelets. The effect of platelets was compared to that of platelet-free supernatants from thrombin-activated platelets that had secreted their active granule constituents. Platelets dose-dependently induced HUVEC proliferation. Platelets preactivated by thrombin induced similar proliferation as did unactivated platelets (proliferation factor = 7 - 8), indicating that preactivation of platelets was not required. Platelets fixed with paraformaldehyde had no effect, suggesting that the platelet mitogenic effect required a mobile, alive membrane. Ketanserine and suramin reduced by at most 30 % the platelet-induced proliferation; supernatants of thrombin-activated platelets caused only minor proliferation (proliferation factor = 2), suggesting that secreted 5-hydroxytryptamine and growth factors poorly contributed to the proliferative effect. When the co-incubation was performed in the presence of an anti P-selectin antibody, the platelet-induced HUVEC proliferation was inhibited. The results suggest that platelet adhesion participate in the control of the endothelial regeneration and that platelet P-selectin is a molecular determinant of the proliferative signal.

Role of chondroitin 4-sulphate as a receptor for polycation induced human platelet aggregation

1. Proteoglycans provide negatively charged sites on the surface of platelets, leukocytes and endothelial cells. Since chondroitin 4-sulphate is the main proteoglycan present on the platelet surface, the role of this molecule in mediating the activation of human platelets by polylysine was studied. 2. Platelets were desensitized with phorbol 12-myristate 13-acetate (PMA, 10 nM) 5 min before the addition of polylysine to platelet-rich plasma (PRP). Changes in the intracellular Ca2+ concentration were measured in fura2-am (2 microM) loaded platelets and protein phosphorylation was assessed by autoradiography of the electrophoretic profile obtained from [32P]-phosphate labelled platelets. The release of dense granule contents was measured in [14C]-5-hydroxytryptamine loaded platelets and the synthesis of thromboxane (TXA2) was assessed by radioimmunoassay. Surface chondroitin 4-sulphate proteoglycan was degraded by incubating platelets with different concentrations of chondroitinase AC (3 min, 37 degrees C). The amount of chondroitin 4-sulphate remaining in the platelets was then quantified after proteolysis and agarose gel electrophoresis. 3. The addition of PMA to PRP before polylysine inhibited the aggregation by 88 +/- 18% (n = 3). Staurosporine (1 microM, 5 min) prevented the PMA-induced inhibition. Chondroitinase AC (4 pu ml-1 to 400 muu ml-1, 3 min) abolished the polylysine-induced aggregation in PRP but caused only a discrete inhibition of ADP-induced aggregation. The concentration of chrondroitin 4-sulphate in PRP (0.96 +/- 0.2 microgram/10(8) platelets, n = 3) and in washed platelets (WP; 0.35 +/- 0.1 microgram/10(8) platelets, n = 3) was significantly reduced following incubation with chondroitinase AC (PRP = 0.63 +/- 0.1 microgram/10(8) platelets and WP = 0.08 +/- 0.06 microgram/10(8) platelets). 4. Washed platelets had a significantly lower concentration of chondroitin 4-sulphate than platelets in PRP. The addition of polylysine to WP induced a rapid increase in light transmission which was not accompanied by TXA2 synthesis or the release of dense granule contents. This effect was not inhibited by sodium nitroprusside (SNP), iloprost, EDTA or the peptide RGDS. This event was accompanied by the discrete phosphorylation of plekstrin and myosin light chain, which were inhibited by staurosporine (10 microM, 10 min). The hydrolysis of platelet surface chondroitin 4-sulphate strongly reduced the polylysine-induced phosphorylation. 5. Our results indicate that polylysine activates platelets through a specific receptor which could be the proteoglycan chondroitin 4-sulphate present on the platelet membrane.

The kinetics of chondroitin 4-sulfate release from stimulated platelets and its relation to thromboxane A2 formation and granule secretion

1. In platelet rich plasma (PRP), chondroitin 4-sulfate release from platelets occurred after stimulation with ADP (5 microM), collagen (5-10 micrograms/ml), or adrenaline (10 microM). Release started within 60 s and maximum release (0.7-2.0 mg/l) was reached within 180 s. TXA2 formation and dense granule release reached a maximum within 90 s after stimulation. 2. Using washed platelets (1.5 x 10(8) cells/ml), the platelet responses were faster. Release of chondroitin 4-sulfate and TXA2 started within 20-30 s after thrombin addition (100 mU/ml). Maximum release was reached within 60 s in both cases. Dense granule release started in the first 5 s of stimulation (34.6 +/- 12.4%) reaching maximum secretion (74.4 +/- 8.7%) within 60 s. 3. Our results demonstrate that maximal chondroitin 4-sulfate release occurs after the dense granule release reaction in both PRP and washed platelets. This observation suggests that chondroitin 4-sulfate is unlikely to be stored in the dense granules but may be stored in the alpha-granules.