共查询到20条相似文献,搜索用时 31 毫秒
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S.C. Hung N.I. Ghali D.L. Venton G.C. Le Breton 《Prostaglandins & other lipid mediators》1982,24(2):195-206
The effects of prostaglandin F2α on human blood platelet function were investigated. PGF2α at 15 μM completely blocked platelet aggregation induced by 500 μM arachidonic acid or 3 μM U46619 but had no effect on aggregatin induced by 7.5 μM ADP. A similar specificity of action was not obtained with either PGI2 or PGE2. Thus concentrations of PGI2 (3 nM) or PGE2 (20 μ M) which inhibited U46619-induced aggregation by 100% also blocked ADP-stimulated aggregation.The inhibitory properties of PGF2α were not related to increases in platelet cAMP, since direct measurement of intracellular cAMP revealed that 15 μ M PGF2α produced no substantial change in cAMP levels. This finding was in direct contrast to results obtained using either PGI2 or PGE2. Both PGI2 (3 nM) and PGE2 (20 μ M) induced significant increases in platelet cAMP levels.The possibility that PGF2α directly interacts at the platelet TXA2/PGH2 receptor was investigated by measuring [3H]PGF2α binding to isolated platelet membranes. It was found that [3H] PGF2α binding reached equilibrium within 30 min at room temperature and could be 90% displaced by addition of 1000 fold excess of unlabelled PGF2α. Furthermore, when 1000 fold excess of either the TXA2/PGH2 “mimetic” U46619 or the TXA2/PGH2 antagonist 13-azaprostanoic acid was added, specific [3H] PGF2α binding was displaced by 95% and 85% respectively. In contrast, the same molar excess of 6-keto-PGF1α, azo analog 1, or TXB2, caused displacement of only 15%, 20% or 25% of the [3H] PGF2α binding. Scatchard analysis indicated that [3H] PGF2α has two binding sites; i.e., a high affinity binding site with an apparent Kd of 50 nM and a low affinity binding site with apparent Kd of 320 nM. These results suggest that the selective inhibition by PGF2α of AA or U46619-induced aggregation may be mediated through interaction at the platelet TXA2/PGH2 receptor. 相似文献
4.
The “in vitro” effects of α-tocopherol, butylhydroxytoluene (BHT) and butylhydroxyanisole (BHA) were studied on aggregation of human platelets induced by collagen and arachidonic acid (AA), on the metabolic conversion of 14C AA through the cyclooxygenase and lipoxygenase pathways and on the formation of thromboxane B2 (TXB2) in washed platelets after stimulation with collagen.Vitamin E completely inhibited AA induced platelet aggregation only at high concentration (mM) and after 10 minutes of preincubation, with limited effects on AA metabolism in platelets and no effect on TXB2 formation from endogenous substrate. BHA completely inhibited platelet aggregation in the 10−6M range, gave 50% inhibition of AA metabolism in the 10−5M range and almost complete inhibition of thromboxane formation in the 10−4M range. BHT was about 100 times less active on platelet aggregation and AA metabolism. The lipoxygenase and cyclooxygenase pathways were differentially affected at low concentrations of BHA and only at concentrations greater than 5×10−5M were both pathways depressed. 相似文献
5.
G.C. Le Breton S.C. Hung N.I. Ghali D.L. Venton 《Prostaglandins & other lipid mediators》1984,27(4):543-551
Previous studies have demonstrated that 13-azaprostanoic acid (13-APA) is a potent and specific antagonist of thromboxane A2/prostaglandin H2 (TXA2/PGH2) at the platelet receptor level. In the present study we evaluated the effects of a new azaprostanoid, 2-(6-carboxyhexyl) cyclopentanone hexylhydrazone (CPH), on human platelet function. This hydrazone was found to completely inhibit arachidonic acid (AA)-induced platelet aggregation at 1 uM CPH. On the other hand, CPH was not an effective inhibitor of PGH2-induced aggregation. Furthermore, 100 uM CPH was completely ineffective in blocking platelet aggregation stimulated by adenosine diphosphate (ADP) or the stable prostaglandin endoperoxide analog U46619 (which presumably acts at the TXA2/PGH2 receptor). Measurement of platelet thromboxane B2 (TXB2) production demonstrated that the primary site-of-action of CPH is at the cyclo-oxygenase level. Thus, CPH inhibited TXB2 formation from AA in a dose-dependent manner (0.1 uM–100 uM CPH)2. In contrast, CPH blocked TXB2 production from PGH2 only at the highest CPH concentration tested, i.e., 100 uM. These results indicate that relative to 13-APA, addition of a second nitrogen at C14 and a double bond between the 12- and 13- positions results in a loss of receptor activity but produces a high affinity for the platelet cyclo-oxygenase. 相似文献
6.
《Bone and mineral》1991,12(1):15-23
Throm☐ane A2 (TXA2) is a powerful promoter of platelet aggregation and smooth muscle contraction. However, this compound is highly unstable and is rapidly hydrated to a more stable metabolite, throm☐ane B2 (TXB2). TXA2 has been considered to be involved in bone resorption, in particular bone loss caused by inflammatory diseases and by orthodontic treatment. However precise mechanisms of bone resorption caused by TXA2 have not yet been proved because of its highly unstable nature.Recently, a chemically stable analogue of TXA2, 9,11-epithio-11,12-methanothrom☐ane A2 (STA2), was successfully synthesized. Using this synthetic compound, we examined its in vitro bone resorbing activity and induction of osteoclast-like cells in a mouse marrow culture system in comparison with related compounds with bone resorbing activity. Like prostaglandin E2 (PGE2), a well-known bone resorbing agent. STA2 time-and dose-dependently stimulated the release of 45Ca from prelabelled mouse calvariae. Both STA2 and PGE2 induced the accumulation of cAMP in mouse calvariae. The TXA2, agonist. ONO-3708, inhibited STA2-induced release of 45Ca, TXB2 induced neither bone resolor cAMP accumulation. When mouse marrow cells were cultured with STA2 for 8 days, osteoclast-like multinucleated cells appeared in parallel with the increase of the amount of STA2 added. Again TXB2 showed no effect on osteoclast-like cell formation. These results indicate a role for TXA2 in some form of bone resorption. 相似文献
7.
J. Bult E. Wechsung A. Houvenaghel A.G. Herman 《Prostaglandins & other lipid mediators》1981,21(6):1045-1058
Aggregation of chicken thrombocytes was studied in whole blood using an electronic aggregometer. Serotonin (5-hydroxytryptamine, 5HT), arachidonic acid (AA) and collagen, but not adenosinediphosphate (ADP) induced aggregation. Prostaglandin (PG) endoperoxides were essential for arachidonic acid-induced aggregation, but were not involved in 5HT-induced aggregation, as indicated by inhibitory studies with indomethacin. Similar experiments indicated that biosynthesis of endogenous PG endoperoxides contributed to the aggregation induced by low concentrations of collagen, but was of little importance when high collagen doses were employed. PGE1 and PGE2 could abolish all types of aggregation studied, whereas prostacyclin (PGI2) and PGD2 were without any anti-aggregatory activity at 1 μg/ml. Between 1 and 100 ng/ml PGE1 and PGE2 inhibited arachidonic acid- and 5HT-induced aggregation dose-dependently.The lack of any hemostatic function of PGI2 in chickens was also indicated by the absence of biosynthesis of endogenous PGI2 in chicken aorta. PGI2 was assessed as anti-aggregating activity, released by aortic fragments stirred in rabbit platelet rich plasma. Still, the presence of chicken aortic tissue i chicken whole blood inhibited 5HT-, but not arachidonic acid-induced aggregation. This inhibition was not affected by pretreatment of the aortic fragments with indomethacin or pargyline. 相似文献
8.
R.J. Gryglewski J.A. Salmon F.B. Ubatuba B.C. Weatherly S. Moncada J.R. Vane 《Prostaglandins & other lipid mediators》1979,18(3):453-478
In human platelet-rich plasma (PRP) eicosapentaenoic acid (EPA) inhibited platelet aggregation induced by a stable analogue of PGH2 (U46619), arachidonic acid, collagen or ADP. EPA was more potent than oleic, linoleic, α-linolenic or γ-linolenic acids. In aspirin-treated platelets, aggregation induced by U46619 was inhibited to a similar extent by arachidonic acid or by EPA over a range of concentrations of 0.05–0.3 mM. EPA incubated with PRP did not induce the generation of a thromboxane (TXA)-like activity; indeed it prevented the formation of TXA2 induced by arachidonic acid or by collagen. The anti-aggregatory activity of EPA was not influenced by inhibitors of cyclo-oxygenase and lipoxygenase. The anti-aggregatory action of EPA may be caused by a rapid occupancy by EPA of TXA2/PGH2 “receptors” on platelet membrane as well as by a slower displacement of arachidonic acid from platelet phospholipids by chemically unchanged molecules of EPA.Not all samples of PRP were irreversibly aggregated by PGH2, but in those that were, PGH3 also induced an immediate dose-dependent but reversible aggregation. After a 4 min incubation of non-aggregating doses of PGH2 or PGH3 (100–300 nM) with PRP a stable anti-aggregatory compound was detected. The inhibitory activity produced from PGH3 was apparently more potent (ca 10 times) than that obtained from PGH2. The anti-aggregating compounds were identified by TLC and GLC-MS as PGD2 and PGD3. The apparent difference of potency between PGD2 and PGD3 was attributed to the concurrent production of PGE2 and PGE3. PGE2 prevented the inhibitory effect of PGD2 whereas PGE3 did not affect the activity of PGD3.It is concluded that one of the reasons for the low incidence of myocardial infarction in Eskimos could be that the pro-aggregatory arachidonic acid is replaced in their phospholipids by the anti-aggregatory EPA. 相似文献
9.
Background
We have shown that 1,2,3,4,6-penta-O-galloyl-α-D-glucopyranose (α-PGG), an orally effective hypoglycemic small molecule, binds to insulin receptors and activates insulin-mediated glucose transport. Insulin has been shown to bind to its receptors on platelets and inhibit platelet activation. In this study we tested our hypothesis that if insulin possesses anti-platelet properties then insulin mimetic small molecules should mimic antiplatelet actions of insulin.Principal Findings
Incubation of human platelets with insulin or α-PGG induced phosphorylation of insulin receptors and IRS-1 and blocked ADP or collagen induced aggregation. Pre-treatment of platelets with α-PGG inhibited thrombin-induced release of P-selectin, secretion of ATP and aggregation. Addition of ADP or thrombin to platelets significantly decreased the basal cyclic AMP levels. Pre-incubation of platelets with α-PGG blocked ADP or thrombin induced decrease in platelet cyclic AMP levels but did not alter the basal or PGE1 induced increase in cAMP levels. Addition of α-PGG to platelets blocked agonist induced rise in platelet cytosolic calcium and phosphorylation of Akt. Administration of α-PGG (20 mg kg−1) to wild type mice blocked ex vivo platelet aggregation induced by ADP or collagen.Conclusions
These data suggest that α-PGG inhibits platelet activation, at least in part, by inducing phosphorylation of insulin receptors leading to inhibition of agonist induced: (a) decrease in cyclic AMP; (b) rise in cytosolic calcium; and (c) phosphorylation of Akt. These findings taken together with our earlier reports that α-PGG mimics insulin signaling suggest that inhibition of platelet activation by α-PGG mimics antiplatelet actions of insulin. 相似文献10.
《Journal of Fermentation and Bioengineering》1991,71(1):12-18
The reaction mechanism of PGE2 biosynthesis was investigated by a detailed examination of the cyclo-oxygenase and PGE2-isomerase activities in acetone-pentane powder (microsomal fraction of ram seminal vesicular glands). Two main types of inactivating process were recognized in the reaction system. One type was due to irreversible inactivation caused by the oxidizing agent [O]·X released through the reduction of PGG2 to PGH2, while the other type was due to reversible inhibition which was supposed to be derived from the precursor arachidonic acid (AA). This inhibitor was found to block the activities of both cyclooxygenase and PGE2-isomerase, and to compete with the substrates AA and PGH2. Although no significant substrate inhibition was observed, arachidonic acid was slightly inhibitory toward PGE2-isomerase. 相似文献
11.
Ca2+ signaling in the transformation of promastigotes to axenic amastigotes of Leishmania donovani 总被引:1,自引:0,他引:1
Rudrammaji LM Machiah KD Kantha TP Gowda TV 《Molecular and cellular biochemistry》2001,219(1-2):39-44
Three acidic phospholipases A2 from Indian cobra (Naja naja naja) venom inhibited platelet aggregation in platelet rich plasma induced separately by ADP, collagen and epinephrine with different potencies. The order of inhibition was epinephrine > collagen > ADP. They did not inhibit platelet aggregation induced by arachidonic acid (10 M). The inhibition was dependent on concentration of the protein and the time of incubation of the phospholipases A2 with platelet rich plasma. Parabromophenacyl bromide modified PLA2 enzymes lost their enzymatic activity as well as platelet aggregation inhibition activity suggesting the involvement of catalytic function in platelet aggregation inhibitory activity. 相似文献
12.
Ryszard J. Gryglewski Stuart Bunting Salvador Moncada Roderick J. Flower John R. Vane 《Prostaglandins & other lipid mediators》1976,12(5):685-713
Prostaglandin (PG) endoperoxides (PGG2 and PGH2) contract arterial smooth muscle and cause platelet aggregation. Microsomes from pig aorta, pig mesenteric arteries, rabbit aorta and rat stomach fundus enzymically transform PG endoperoxides to an unstable product (PGX) which relaxes arterial strips and prevents platelet aggregation. Microsomes from rat stomach corpus, rat liver, rabbit lungs, rabbit spleen, rabbit brain, rabbit kidney medulla, ram seminal vesicles as well as particulate fractions of rat skin homogenates transform PG endoperoxides to PGE- and PGF- rather than to PGX-like activity.PGX differs from the products of enzymic transformation of prostaglandin endoperoxides so far identified, including PGE2, F2α, D2, thromboxane A2 and their metabolites.PGX is less active in contracting rat fundic strip, chick rectum, guinea pig ileum and guinea pig trachea than are PGG2 and PGH2. PGX does not contract the rat colon.PGX is unstable in aqueous solution and its anti-aggregating activity disappears within 0.25 min on boiling or within 10 min at 37° C.As an inhibitor of human platelet aggregation induced by arachidonic acid PGX was 30 times more potent than PGE1. The enzymic formation of PGX is inhibited by 15-hydroperoxy arachidonic acid (IC50 = 0.48 μg/ml), by spontaneously oxidised arachidonic acid (IC50 <100 μg/ml) and by tranylcypromine (IC50 = 160 μg/ml).We conclude that a balance between formation by arterial walls of PGX which prevents platelet aggregation and release by blood platelets of prostaglandin endoperoxides which induce aggregation is of the utmost importance for the control of thrombus formation in vessels. 相似文献
13.
The present study was undertaken in order to characterize the dose-dependent nature of acetylsalicylic acid (ASA) on platelet aggregation and plasma thromboxane B2 (TXB2) release in healthy volunteers. Volunteers received either 25, 50, 100 or 500 mg daily for five consecutive days. At the end of the five day period, all dosages of ASA were capable of completely suppressing TXB2 production and arachidonic acid-induced platelet aggregation. At that time, the second phase of ADP-induced aggregation was also blocked. However, while the inhibition following 500 mg ASA was complete after 24 hours, total inhibition with 100, 50 and 25 mg was attained only after two, three and four days, respectively, indicating the cumulative effect of ASA on platelets. Aggregation induced by collagen was also inhibited dose-dependently- yet slower and at no time complete. ASA had no inhibitory effect on aggregation by platelet-activating factor (PAF). It is concluded that a daily dose of 50 mg ASA would suffice in blocking platelet TXA2 production and aggregation induced by most physiological agents. 相似文献
14.
Maurice B. Feinstein Elmer L. Becker Carol Fraser 《Prostaglandins & other lipid mediators》1977,14(6):1075-1093
The formation of malondialdehyde (MDA) and rabbit aorta contracting substance (RCS) induced by treatment of platelets with thrombin and collagen, but not that produced from exogenous arachidonic acid, is inhibited by prostaglandin E1 (10−8 − 10−7M), the local anesthetics tetracaine, SKF 525-A and dibucaine (1 mM), and the serine-protease inhibitor phenylmethanesulfonyl fluoride (PMSF). The burst in oxygen consumption which accompanies platelet stimulation by thrombin and collagen in the presence of antimycin A, known to be due to the oxidation of endogenous arachidonate, is also markedly suppressed by PGE1, tetracaine and PMSF. The inhibitory effect of PGE1 is strongly potentiated by theophylline (1.0 mM).Addition of the Ca2+ ionophore A23187 to platelet suspensions overcomes PGE1 and PMSF inhibition of MDA and RCS formation, and induces a vigorous increase in O2 consumption. Tetracaine and dibucaine, however, block the responses to A23187.Formation of MDA and RCS (a mixture of PG endoperoxides and TXA2) due to stimulation by thrombin and collagen depends upon activation of Ca2+-dependent phospholipase A2 (PLA2) to supply free arachidonate from specific membrane phospholipids. These experiments therefore indicate that increased cellular cAMP, induced by PGE1, antagonizes the mobilization of the Ca2+ which is normally required for PLA2 activity. Thrombin-stimulated platelets exhibit enhanced 45Ca uptake which probably reflects exchange of extracellular Ca2+ with an increased available pool of exchangeable intracellular Ca2+. PGE1 strongly suppresses this 45Ca uptake, providing more direct evidence supporting the view that cAMP prevents the rise in free cytoplasmic Ca2+ induced by thrombin. Under conditions which make sufficient free cytoplasmic Ca2+ available (i.e., A23187), despite high cellular cAMP, formation of RCS and MDA, and O2 uptake are nearly normal indicating that activation of PLA2 can occur. Local anesthetics on the other hand since they abolish the response to A23187 as well, appear to directly antagonize the ability of Ca2+ to activate PLA2. The effect of PMSF suggests that stimulus-specific proteases may be involved in the thrombin and collagen-induced activation of PLA2 activity. 相似文献
15.
Prostaglandin (PG) E2, thromboxane (TX) B2 and the stable breakdown product of prostacyclin, 6-oxo-PGF1α are present in carrageenin-induced inflammatory exudates. Carrageenin-impregnated polyester sponges were implanted subcutaneously in rats and inflammatory exudates were collected 4–192 h after implantation. The concentrations of cyclo-oxygenase products in sponge fluids was measured by radioimmunoassay after extraction and purification. All three products were detectable after 4 h and reached a peak at 12–24 h. Mean TXB2 concentrations reached 74 ng/ml at 12 h but decreased to less than 10 ng/ml after 24 h. PGE2 concentrations were 65 ng/ml at 24 h, after which there was no significant increase and then dropped to about 20 ng/ml between 96 and 192 h. 6-oxo-PGF1α reached a concentration of 33 ng/ml at 24 h which did not change significantly until levels fell to less than 10 ng/ml between 96 and 192 h. The presence of PGE2, TXB2 and 6-oxo-PGF1α was confirmed by gas-liquid chromatography and mass spectrometry. Total leukocyte numbers increased steadily and were at their highest (116.0 × 106 cells/ml) at 192 h. These results suggest that thromboxanes and prostacyclin, as well as PGE2, contribute to the acute inflammatory response. 相似文献
16.
Roger W. Hunter Carol MacKintosh Ingeborg Hers 《The Journal of biological chemistry》2009,284(18):12339-12348
The elevation of [cAMP]i is an important mechanism of
platelet inhibition and is regulated by the opposing activity of adenylyl
cyclase and phosphodiesterase (PDE). In this study, we demonstrate that a
variety of platelet agonists, including thrombin, significantly enhance the
activity of PDE3A in a phosphorylation-dependent manner. Stimulation of
platelets with the PAR-1 agonist SFLLRN resulted in rapid and transient
phosphorylation of PDE3A on Ser312, Ser428,
Ser438, Ser465, and Ser492, in parallel with
the PKC (protein kinase C) substrate, pleckstrin. Furthermore, phosphorylation
and activation of PDE3A required the activation of PKC, but not of PI3K/PKB,
mTOR/p70S6K, or ERK/RSK. Activation of PKC by phorbol esters also resulted in
phosphorylation of the same PDE3A sites in a PKC-dependent, PKB-independent
manner. This was further supported by the finding that IGF-1, which strongly
activates PI3K/PKB, but not PKC, did not regulate PDE3A. Platelet activation
also led to a PKC-dependent association between PDE3A and 14-3-3 proteins. In
contrast, cAMP-elevating agents such as PGE1 and forskolin-induced
phosphorylation of Ser312 and increased PDE3A activity, but did not
stimulate 14-3-3 binding. Finally, complete antagonism of
PGE1-evoked cAMP accumulation by thrombin required both
Gi and PKC activation. Together, these results demonstrate that
platelet activation stimulates PKC-dependent phosphorylation of PDE3A on
Ser312, Ser428, Ser438, Ser465,
and Ser492 leading to a subsequent increase in cAMP hydrolysis and
14-3-3 binding.Upon vascular injury, platelets adhere to the newly exposed subintimal
collagen and undergo activation leading to platelet spreading to cover the
damaged region and release of thrombogenic factors such as ADP and thromboxane
A2. In addition, platelets are activated by thrombin, which is
generated as a result of activation of the coagulation pathway, and stimulates
platelets by cleaving the protease-activated receptors
(PAR),2
PAR-1 and PAR-4. The final common pathway is the exposure of fibrinogen
binding sites on integrin αIIbβ3 resulting in
platelet aggregation and thrombus formation.Thrombin-mediated cleavage of PARs leads to activation of phospholipase C
β (PLC), hydrolysis of phosphatidylinositol (PI) 4,5-bisphosphate and a
subsequent increase in [Ca2+]i and activation
of protein kinase C (PKC). Protein kinase C contributes to platelet activation
both directly, through affinity regulation of the fibrinogen receptor,
integrin αIIbβ3
(1), and indirectly by
enhancing degranulation (2).
Thrombin also stimulates activation of PI 3-kinases and subsequent generation
of PI (3,
4,
5) trisphosphate and PI
(3,
4) bisphosphate
(3), which recruit protein
kinase B (PKB) to the plasma membrane where it becomes phosphorylated and
activated.Platelet activation is opposed by agents that raise intracellular
3′-5′-cyclic adenosine monophosphate
([cAMP]i). cAMP is a powerful inhibitory second messenger
that down-regulates platelet function by interfering with Ca2+
homeostasis, degranulation and integrin activation
(4). Synthesis of cAMP is
stimulated by mediators such as prostaglandin I2 (PGI2),
which bind to Gs-coupled receptors leading to activation of
adenylate cyclase (AC). This inhibitory pathway is opposed by thrombin, which
inhibits the elevation of cAMP indirectly via autocrine activation of the
Gi-coupled ADP receptor P2Y12. cAMP signaling is
terminated by hydrolysis to biologically inert 5′-AMP by
3′-phosphodiesterases. Platelets express two cAMP phosphodiesterase
isoforms, cGMP-stimulated PDE2 and cGMP-inhibited PDE3A. PDE3A is the most
abundant isoform in platelets and has a ∼250-fold lower
Km for cAMP than PDE2
(4). As a consequence of these
properties, PDE3A exerts a greater influence on cAMP homeostasis, particularly
at resting levels. The importance of PDE3A in platelet function is further
emphasized by the finding that the PDE3A inhibitors cilostamide and milrinone
raise basal cAMP levels and strongly inhibit thrombin-induced platelet
activation (5). Furthermore,
PDE3A-/- mice demonstrate increased resting levels of platelet cAMP
and are protected against a model of pulmonary thrombosis
(6). In contrast, the PDE2
inhibitor EHNA has no significant effect on cAMP levels and platelet
aggregation (7,
8). The activity of PDE3A is
therefore essential to maintain low equilibrium levels of cAMP and determine
the threshold for platelet activation
(7).Like its paralogue PDE3B, it has recently become clear that PDE3A activity
can be positively regulated by phosphorylation in platelets and human oocytes
(9,
10). There is some evidence
that PKB may be involved in this regulation, although the phosphorylation
sites are poorly characterized. In contrast, phosphorylation of PDE3A in HeLa
cells was stimulated by phorbol esters and blocked by inhibitors of PKC
(11). In this study, we aimed
to identify the signaling pathways and phosphorylation sites that are involved
in regulation of platelet PDE3A. Here, we show strong evidence that PKC, and
not PKB, is involved in agonist-stimulated PDE3A phosphorylation on
Ser312, Ser428, Ser438, Ser465,
and Ser492, leading to an increase in PDE3A activity, 14-3-3
binding and modulation of intracellular cAMP levels. 相似文献
17.
Yi Chang Steven Kuan-Hua Huang Wan-Jung Lu Chi-Li Chung Wei-Lin Chen Shun-Hua Lu Kuan-Hung Lin Joen-Rong Sheu 《Journal of biomedical science》2013,20(1):1-11
Background
Brazilin, isolated from the heartwood of Caesalpinia sappan L., has been shown to possess multiple pharmacological properties.Methods
In this study, platelet aggregation, flow cytometry, immunoblotting analysis, and electron spin resonance (ESR) spectrometry were used to investigate the effects of brazilin on platelet activation ex vivo. Moreover, fluorescein sodium-induced platelet thrombi of mesenteric microvessels was also used in in vivo study.Results
We demonstrated that relatively low concentrations of brazilin (1 to 10 μM) potentiated platelet aggregation induced by collagen (0.1 μg/ml) in washed human platelets. Higher concentrations of brazilin (20 to 50 μM) directly triggered platelet aggregation. Brazilin-mediated platelet aggregation was slightly inhibited by ATP (an antagonist of ADP). It was not inhibited by yohimbine (an antagonist of epinephrine), by SCH79797 (an antagonist of thrombin protease-activated receptor [PAR] 1), or by tcY-NH2 (an antagonist of PAR 4). Brazilin did not significantly affect FITC-triflavin binding to the integrin αIIbβ3 in platelet suspensions. Pretreatment of the platelets with caffeic acid phenethyl ester (an antagonist of collagen receptors) or JAQ1 and Sam.G4 monoclonal antibodies raised against collagen receptor glycoprotein VI and integrin α2β1, respectively, abolished platelet aggregation stimulated by collagen or brazilin. The immunoblotting analysis showed that brazilin stimulated the phosphorylation of phospholipase C (PLC)γ2 and Lyn, which were significantly attenuated in the presence of JAQ1 and Sam.G4. In addition, brazilin did not significantly trigger hydroxyl radical formation in ESR analysis. An in vivo mouse study showed that brazilin treatment (2 and 4 mg/kg) significantly shortened the occlusion time for platelet plug formation in mesenteric venules.Conclusion
To the best of our knowledge, this study provides the first evidence that brazilin acts a novel collagen receptor agonist. Brazilin is a plant-based natural product, may offer therapeutic potential as intended anti-thrombotic agents for targeting of collagen receptors or to be used a useful tool for the study of detailed mechanisms in collagen receptors-mediated platelet activation. 相似文献18.
Prostaglandin (PG) E2, thromboxane (TX) B2 and the stable breakdown product of prostacyclin, 6-oxo-PGF1α are present in carrageenin-induced inflammatory exudates. Carrageenin-impregnated polyester sponges were implanted subcutaneously in rats and inflammatory exudates were collected 4–192 h after implantation. The concentrations of cyclo-oxygenase products in sponge fluids was measured by radioimmunoassay after extraction and purification. All three products were detectable after 4 h and reached a peak at 12–24 h. Mean TXB2 concentrations reached 74 ng/ml at 12 h but decreased to less than 10 ng/ml after 24 h. PGE2 concentrations were 65 ng/ml at 24 h, after which there was no significant increase and then dropped to about 20 ng/ml between 96 and 192 h. 6-oxo-PGF1α reached a concentration of 33 ng/ml at 24 h which did not change significantly until levels fell to less than 10 ng/ml between 96 and 192 h. The presence of PGE2, TXB2 and 6-oxo-PGF1α was confirmed by gas-liquid chromatography and mass spectrometry. Total leukocyte numbers increased steadily and were at their highest (116.0 × 106 cells/ml) at 192 h. These results suggest that thromboxanes and prostacyclin, as well as PGE2, contribute to the acute inflammatory response. 相似文献
19.
Edward E. Nishizawa William L. Miller Robert R. Gorman Gordon L. Bundy Jan Svensson Mats Hamberg 《Prostaglandins & other lipid mediators》1975,9(1)
Prostaglandin D2 was found to be a potent inhibitor of platelet aggregation. Aggregation of human platelets by ADP, collagen and prostaglandin G2 was inhibited more strongly by PGD2 than by PGE1. Although ADP-induced aggregation of rabbit platelets was inhibited more strongly by PGE1 than by PGD2 the latter prostaglandin gave a more long-lasting inhibitory effect on platelet aggregation following intravenous or oral administration. These results coupled with the finding that PGD2 has less hypotensive effects on the cardiovascular system than PGE1 suggest the possible use of PGD2 as an antithrombotic agent. 相似文献
20.
Prostaglandin D2 was found to be a potent inhibitor of platelet aggregation. Aggregation of human platelets by ADP, collagen and prostaglandin G2 was inhibited more strongly by PGD2 than by PGE1. Although ADP-induced aggregation of rabbit platelets was inhibited more strongly by PGE1 than by PGD2 the latter prostaglandin gave a more long-lasting inhibitory effect on platelet aggregation following intravenous or oral administration. These results coupled with the finding that PGD2 has less hypotensive effects on the cardiovascular system than PGE1 suggest the possible use of PGD2 as an antithrombotic agent. 相似文献