Mechanism of Action of p-Chlorobiphenyl on the Inhibition of Platelet Aggregation

p-Chlorobiphenyl (1–50 μm ) concentration-dependently inhibited the aggregation and release reaction of rabbit washed platelets induced by arachidonic acid and collagen, but not those induced by platelet-activating factor (PAF), U46619 and thrombin. The IC50 values of p-chlorobiphenyl on the arachidonic acid and collagen-induced platelet aggregation were 2.9 ± 0.5 and 12.8 ± 2.3 μm , respectively. The formation of both platelet thromboxane B₂ and prostaglandin D₂ caused by arachidonic acid was inhibited by p-chlorobiphenyl concentration-dependently. In myo-[³H]inositol-labeled and fura-2-loaded platelets, [³H]inositol monophosphate generation and the rise in intracellular Ca²⁺ stimulated by arachidonic acid were inhibited by p-chlorobiphenyl. In human platelet-rich plasma, p-chlorobiphenyl and indomethacin prevented the secondary aggregation and blocked ATP release from platelets induced by adenosine 5′-diphosphate and adrenaline without affecting the primary aggregation. It is concluded that p-chlorobiphenyl may be a cyclo-oxygenase inhibitor and its antiplatelet action is mainly due to the inhibition of thromboxane formation.     

Novel inhibitory actions on platelet thromboxane and inositolphosphate formation by xanthones and their glycosides

Xanthones and their glycosides were tested for their antiplatelet activities in washed rabbit platelets. Tripteroside acetate and norathyriol acetate were the most potent inhibitors. Tripteroside acetate inhibited platelet aggregation and ATP release induced by ADP, arachidonic acid, platelet-activating factor (PAF), collagen, ionophore A23187 and thrombin. The IC50 values of tripteroside acetate toward arachidonic acid- (100 microM) and collagen- (10 micrograms/ml) induced platelet aggregation were 10 and 30 micrograms/ml respectively. It inhibited thromboxane B2 formation of washed platelets caused by arachidonic acid, collagen, thrombin and ionophore A23187 and also that caused by the incubation of lysed platelet homogenate with arachidonic acid. Tripteroside acetate decreased the formation of inositolphosphate caused by thrombin, collagen and PAF, whereas it had no direct effect on fibrinogen-platelet interaction. It is concluded that xanthone derivatives inhibited platelet aggregation and release reaction by diminishing thromboxane formation and phosphoinositide breakdown.     

Inhibition of Platelet Thromboxane Formation and Phosphoinositides Breakdown by Diisoeugenol

Abstract— Diisoeugenol inhibited the platelet aggregation and ATP release of rabbit platelets caused by ADP, arachidonic acid, platelet-activating factor (PAF), collagen and thrombin. Prolongation of the incubation time of platelets with diisoeugenol did not cause further inhibition and the aggregability of platelets could not be restored after washing. In human platelet-rich plasma, diisoeugenol inhibited the biphasic aggregation and ATP release induced by adrenaline and ADP in a concentration-dependent manner. Thromboxane B₂ formation caused by arachidonic acid, collagen and thrombin was markedly inhibited by diisoeugenol in a concentration-dependent manner. Diisoeugenol also inhibited the formation of inositol monophosphate caused by collagen, PAF and thrombin. The cAMP level of washed platelets was not changed by diisoeugenol. It is concluded that the antiplatelet effect of diisoeugenol is due to the inhibition of thromboxane formation and phosphoinositides breakdown.     

Bakkenolide G,a Natural PAF-receptor Antagonist

Because platelet-activating factor (PAF, 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine) participates in many physiopathological responses, including inflammatory reaction, endotoxic shock, allergic diseases and platelet aggregation, PAF-receptor antagonists are important in the treatment of these diseases. A biologically active compound, bakkenolide G, extracted from the plant Petasites formosanus selectively and concentration-dependently inhibited PAF-induced platelet aggregation and ATP release. The IC50 of bakkenolide G for PAF (2 ng mL^?1)-induced platelet aggregation was 5.6 ± 0.9 μm . Bakkenolide G also concentration-dependently inhibited PAF-induced intracellular signal transductions, including thromboxane B₂ formation, and increased intra-cellular calcium concentration and phosphoinositide breakdown without affecting those caused by thrombin (01 units mL^?1), collagen (10 μg mL^?1), arachidonic acid (100 μm ) and U46619 (1 μm ). Bakkenolide G shifted the concentration-response curves of PAF-induced platelet aggregation parallel to the right; the Schild plot slope and the pA₂ value were 1.31 ± 0.31 and 6.21 ± 0.75, respectively. Moreover, bakkenolide G concentration-dependently competed with [³H]PAF binding to platelets, with an IC50 value of 2.5 ± 0.4 μm . These data strongly indicate that bakkenolide G is a specific PAF-receptor antagonist as an antiplatelet aggregatory agent.     

Dicentrine, a novel antiplatelet agent inhibiting thromboxane formation and increasing the cyclic AMP level of rabbit platelets.

Dicentrine is an antiplatelet agent isolated from the Chinese herb Lindera megaphylla. We examined the in vitro effects of dicentrine on various aspects of platelet reactivity. Dicentrine inhibited the aggregation and ATP release of washed rabbit platelets induced by arachidonic acid (AA), collagen, ADP, platelet-activating factor (PAF), thrombin and U46619. Dicentrine also inhibited the thromboxane B2 formation caused by AA, collagen and thrombin in washed intact platelets or that induced by AA in lysed platelet homogenate, while prostaglandin D2 formation caused by AA was not increased. The generation of inositol monophosphates (in the presence of indomethacin) caused by thrombin, collagen and PAF was not suppressed significantly, nor did dicentrine suppress fibrinogen-induced aggregation of elastase-treated platelets. Dicentrine inhibited the intracellular Ca2+ increase in quin-2/AM-loaded platelets caused by thrombin, PAF, collagen and AA. The cyclic AMP level was elevated by dicentrine in a concentration-dependent manner. These data indicate that the inhibitory effect of dicentrine on platelet aggregation and ATP release was due to the inhibition of thromboxane formation and the elevation of the level of cyclic AMP.     

Antiplatelet Effects of Some Aporphine and Phenanthrene Alkaloids in Rabbits and Man

Two aporphines (boldine and laurolitsine) and five phenanthrene alkaloids (litebamine, secoboldine, N-cyanosecoboldine, N-methylsecoglaucine and N-methylsecopredicentrine) were evaluated in-vitro for their ability to inhibit platelet aggregation. All seven alkaloids inhibited aggregation of rabbit platelets and inhibited the release of ATP induced by arachidonic acid and collagen in rabbit platelets. Those aggregations induced by platelet-activating factor (PAF), thrombin, U46619 and ADP were inhibited by the three N-substituted secoboldine derivatives only. Thromboxane B₂ formation caused by arachidonic acid was also suppressed by these compounds. They did not affect the generation of [³H]inositol monophosphate caused by collagen, PAF and thrombin in the presence of indomethacin. Platelet cyclic AMP level was unaffected by litebamine, but was increased by N-methyl-secoglaucine. Litebamine suppressed the secondary aggregation, but not the primary aggregation, induced by ADP and adrenaline in platelet-rich plasma from man, whereas N-methylsecoglaucine inhibited both primary and secondary aggregation. It is concluded that the antiplatelet effect of these seven aporphine and phenanthrene alkaloids is mainly a result of inhibition of thromboxane A₂ formation; N-methylsecoglaucine has additional antiplatelet activity as a result of increasing the levels of platelet cyclic AMP.     

Antiplatelet effect of marchantinquinone, isolated from Reboulia hemisphaerica, in rabbit washed platelets

Platelet activation is involved in serious pathological situations, including atherosclerosis and restenosis. It is important to find efficient antiplatelet medicines to prevent fatal thrombous formation during the course of these diseases. Marchantinquinone, a natural compound isolated from Reboulia hemisphaerica, inhibited platelet aggregation and ATP release stimulated by thrombin (0.1 units mL(-1)), platelet-activating factor (PAF; 2 ng mL(-1)), collagen (10 microg mL(-1)), arachidonic acid (100 microM), or U46619 (1 microM) in rabbit washed platelets. The IC50 values of marchantinquinone on the inhibition of platelet aggregation induced by these five agonists were 62.0 +/- 9.0, 86.0 +/- 7.8, 13.6 +/- 4.7, 20.9 +/- 3.1 and 13.4 +/- 5.3 microM, respectively. Marchantinquinone inhibited thromboxane B2 (TxB2) formation induced by thrombin, PAF or collagen. However, marchantinquinone did not inhibit TxB2 formation induced by arachidonic acid, indicating that marchantinquinone did not affect the activity of cyclooxygenase and thromboxane synthase. Marchantinquinone did inhibit the rising intracellular Ca2+ concentration stimulated by the five platelet-aggregation inducers. The formation of inositol monophosphate induced by thrombin was inhibited by marchantinquinone. Platelet cAMP and cGMP levels were unchanged by marchantinquinone. The results indicate that marchantinquinone exerts antiplatelet effects by inhibiting phosphoinositide turnover.     

Studies on the Synthesis of Some Xanthonoid Derivatives Possessing Antiplatelet Effects

Abstract— 2,3- and 3,4-Dihydroxyxanthone react with ethyl 2,3-dibromopropanoate to form the new, substituted 1,4-benzodioxanes 3 and 4, respectively. The regioisomers 3a and 3b; 4a and 4b were separated by column chromatography and characterized for evaluation of the antiplatelet effects in rabbit washed platelets and human platelet-rich plasma. The ethoxycarbonyl derivatives 3a (20 μm ) and 3b (20 μm ) strongly inhibited the aggregation of rabbit washed platelets induced by arachidonic acid and collagen. The compound 4b showed the most potent inhibition of rabbit washed-platelet aggregation induced by arachidonic acid (IC50 = 8·3 μm ). Of the compounds tested in human platelet-rich plasma, compound 4b exhibited the most potent inhibition of primary and secondary aggregation induced by adrenaline (IC50 = 8·6 μm ). We conclude that the antiplatelet effects of these four ethoxycarbonyl derivatives are mainly due to an inhibitory effect on thromboxane formation and interference in the adrenaline-receptor interaction.     

Antiplatelet effects of KW-7, a new inhibitor of cyclic nucleotide phosphodiesterases

The antiplatelet effect of a new synthetic compound, 8,9-dimethoxyl-1-(4-methoxy-phenyl)-5,6-dihydro-pyrrolo[2,1-a]isoquinoline-2,3-dione (KW-7), was determined in rabbit platelets. KW-7 concentration-dependently prevented platelet aggregation caused by arachidonic acid, collagen, platelet-activating factor, and thrombin. KW-7 induced a substantial increase in cyclic AMP levels and a smaller increase in cyclic GMP levels in platelets. In platelet homogenates, KW-7 inhibited both cyclic AMP- and cyclic GMP-phosphodiesterase activities. The antiplatelet effect of KW-7 was reversed by SQ22536 (an inhibitor of adenylate cyclase) and H89 (an inhibitor of protein kinase A) but not by ODQ (an inhibitor of soluble guanylate cyclase). These data suggest that the antiplatelet effect of KW-7 is cyclic AMP-dependent, and is through inhibition of platelet phosphodiesterases. In addition, KW-7 inhibited arachidonic acid-stimulated thromboxane production; this effect was associated with an increase in prostaglandin D(2) levels indicating KW-7 is also an inhibitor of thromboxane synthase. The dual inhibition of KW-7 on phosphodiesterase and thromboxane synthase might provide an attractive target in developing antiplatelet drugs.     

The dopamine D(1) receptor agonist SKF-82958 serves as a discriminative stimulus in the rat

The antiplatelet effect of the pyridazinone analogue, 4, 5-dihydro-6-[4-[2-hydroxy-3-(3,4 dimethoxybenzylamino)propoxy]naphth-1-yl]-3(2H)-pyridazinone (HCL-31D), was investigated in vitro with rabbit platelets. HCL-31D dose-dependently inhibited the platelet aggregation and ATP release induced by collagen (10 microg/ml), arachidonic acid (100 microM) or thrombin (0.1 U/ml) with an IC(50) of about 0.95-5.41 microM. HCL-31D (0.5-5 microM) increased the platelet cyclic AMP level in a dose-dependent manner. Furthermore, HCL-31D potentiated cyclic AMP formation caused by prostaglandin E(1) but not that caused by 3-isobutyl-1-methylxanthine (IBMX). HCL-31D also attenuated phosphoinositide breakdown and intracellular Ca(2+) elevation induced by collagen, arachidonic acid or thrombin. HCL-31D inhibited the formation of thromboxane B(2) induced by collagen or thrombin but not by arachidonic acid. In addition, HCL-31D did not affect platelet cylooxygenase and thromboxane synthase activity. These data indicate that HCL-31D is an inhibitor of phosphodiesterase and that its antiplatelet effect is mainly mediated by elevation of cyclic AMP levels.     

Antiplatelet activity of [5-(2-methoxy-5-chlorophenyl)furan-2-ylcarbonyl]guanidine (KR-32570), a novel sodium/hydrogen exchanger-1 and its mechanism of action

The antiplatelet effects of a novel guanidine derivative, KR-32570 ([5-(2-methoxy-5-chlorophenyl) furan-2-ylcarbonyl]guanidine), were investigated with an emphasis on the mechanisms underlying its inhibition of collagen-induced platelet aggregation. KR-32570 significantly inhibited the aggregation of washed rabbit platelets induced by collagen (10 microg/mL), thrombin (0.05 U/mL), arachidonic acid (100 microM), a thromboxane (TX) A2 mimetic agent U46619 (9,11-dideoxy-9,11-methanoepoxy-prostaglandin F2, 1 microM) and a Ca2+ ATPase inhibitor thapsigargin (0.5 microM) (IC50 values: 13.8 +/- 1.8, 26.3 +/- 1.2, 8.5 +/- 0.9, 4.3 +/- 1.7 and 49.8 +/- 1.4 microM, respectively). KR-32570 inhibited the collagen-induced liberation of [3H]arachidonic acid from the platelets in a concentration dependent manner with complete inhibition being observed at 50 microM. The TXA2 synthase assay showed that KR-32570 also inhibited the conversion of the substrate PGH2 to TXB2 at all concentrations. Furthermore, KR-32570 significantly inhibited the [Ca2+]i mobilization induced by collagen at 50 microM, which is the concentration that completely inhibits platelet aggregation. KR-32570 also decreased the level of collagen (10 microg/mL)-induced secretion of serotonin from the dense-granule contents of platelets, and inhibited the NHE-1-mediated rabbit platelet swelling induced by intracellular acidification. These results suggest that the antiplatelet activity of KR-32570 against collagen-induced platelet aggregation is mediated mainly by inhibiting the release of arachidonic acid, TXA2 synthase, the mobilization of cytosolic Ca2+ and NHE-1.     

2-(2-Br-phenyl)-8-methoxy-benzoxazinone (HPW-RX2), a direct thrombin inhibitor with a suppressive effect on thromboxane formation in platelets

2-(2-Br-phenyl)-8-methoxy-benzoxazinone (HPW-RX2), a newly synthetic benzoxazinone derivative, has previously been shown to inhibit rabbit platelet aggregation caused by thrombin and arachidonic acid. In the present study, the mechanism for the antiplatelet effect of HPW-RX2 was further investigated. In human platelets, HPW-RX2 concentration-dependently inhibited platelet aggregation, ATP release, P-selectin expression, and intracellular calcium mobilization caused by thrombin. In contrast, HPW-RX2 had no significant effect on either SFLLRN- or GYPGKF-induced platelet aggregation, indicating that HPW-RX2 did not interfere with platelet thrombin receptors. Moreover, HPW-RX2 inhibited the amidolytic activity of thrombin and prolonged the fibrinogen clotting time. These results suggest that the inhibitory effect of HPW-RX2 on thrombin-induced platelet aggregation is via direct inhibition of thrombin proteolytic activity. Besides the inhibition on thrombin, HPW-RX2 also prevented platelet aggregation, ATP release, and increase in [Ca2+]i caused by arachidonic acid and low concentration collagen. In a parallel manner, both arachidonic acid-induced thromboxane B2 and prostaglandin D2 formations were decreased in platelets treated with HPW-RX2. This indicates that HPW-RX2 is able to inhibit the arachidonic acid cascade at the cyclooxygenase level. This is the first report of a benzoxazinone derivative possessing both thrombin and cyclooxygenase inhibitory properties. The dual effect of HPW-RX2 might provide extra therapeutic benefits for treatment of arterial thrombosis.     

An antithrombotic agent, NQ301, inhibits thromboxane A2 receptor and synthase activity in rabbit platelets

In previous studies we have reported that NQ301, a synthetic 1,4-naphthoquinone derivative, displays a potent antithrombotic activity, and that this might be due to antiplatelet effect, which was mediated by the inhibition of cytosolic Ca(2+) mobilization in activated platelets. In the present study, the effect of NQ301 on arachidonic acid cascade in activated platelets has been examined. NQ301 concentration-dependently inhibited washed rabbit platelet aggregation induced by collagen (10 microg/ml), arachidonic acid (100 microM) and U46619 (1 microM), a thromboxane A2 receptor agonist, with IC50 values of 0.60+/-0.02, 0.78+/-0.04 and 0.58+/-0.04 microM, respectively. NQ301 also produced a shift to the right of the concentration-effect curve of U46619, indicating a competitive type of antagonism on thromboxane A2/prostaglandin H2 receptor. NQ301 slightly inhibited collagen-induced arachidonic acid liberation. In addition, NQ301 potently suppressed thromboxane B2 formation by platelets that were exposed to arachidonic acid in a concentration-dependent manner, but had no effect on the production of prostaglandin D2, indicating an inhibitory effect on thromboxane A2 synthase. This was supported by thromboxane A2 synthase activity assay that NQ301 concentration-dependently inhibited thromboxane B2 formation converted from prostaglandin H2. Moreover, NQ301 concentration-dependently inhibited 12-hydroxy-5,8,10,14-eicosatetraenoic acid formation by platelets that were exposed to arachidonic acid. Taken together, these results suggest that NQ301 has a potential to inhibit thromboxane A2 synthase activity with thromboxane A2/prostaglandin H2 receptor blockade, and modulate arachidonic acid liberation as well as 12-hydroxy-5,8,10,14-eicosatetraenoic acid formation in platelets. This may also be a convincing mechanism for the antithrombotic action of NQ301.     

Antiplatelet Mechanism of 2‐Chloro‐3‐(4‐hexylphenyl)‐amino‐1,4‐naphthoquinone (NQ304), an Antithrombotic Agent

Abstract: The effects of 2‐chloro‐3‐(4‐hexylphenyl)‐amino‐1,4‐naphthoquinone (NQ304), an antithrombotic agent, on aggregation, binding of fibrinogen to glycoprotein IIb/IIIa and intracellular signals were investigated using human platelets. NQ304 inhibited thrombin‐, arachidonic acid‐ and thapsigargin‐induced aggregation of washed human platelets with the IC₅₀ values of 22.2±0.7, 6.5±0.2, and 7.6±0.1 μM, respectively. NQ304 significantly inhibited fluorescein isothiocyanate‐conjugated fibrinogen binding to human platelet surface glycoprotein IIb/IIIa receptor by 75%, but failed to inhibit the fibrinogen binding to purified glycoprotein IIb/IIIa receptor. This result suggests that NQ304 inhibit platelet aggregation by suppression of an intracellular pathway that involves exposure of the glycoprotein IIb/IIIa receptor, rather than by direct inhibition of fibrinogen‐glycoprotein IIb/IIIa binding. NQ304 significantly inhibited thrombin‐induced increase in intracellular Ca²⁺ mobilization at the dose of 30 μM and ATP secretion in a dose‐dependent manner. It also inhibited thrombin‐ and arachidonic acid‐induced thromboxane A₂ formation in human platelet dose‐dependently. In conclusion, the antiplatelet mechanism of NQ304 may be due to the reduction of the thromboxane A₂ formation, inhibition of adenosine triphosphate release and intracellular calcium mobilization.     

Antiplatelet effects of piplartine,an alkamide isolated from Piper tuberculatum: possible involvement of cyclooxygenase blockade and antioxidant activity

Objectives Piplartine (piperlongumine; 5,6‐dihydro‐1‐[1‐oxo‐3‐(3,4,5‐trimethoxyphenyl]‐2(1H) pyridinone) is an alkaloid amide isolated from Piper species (Piperaceae). It has been reported to show multiple pharmacological activities in vitro and in vivo. Methods We evaluated the in‐vitro antiplatelet effect of piplartine isolated from the roots of P. tuberculatum, on human platelet aggregation induced in platelet‐rich plasma by the agonists collagen, adenosine 5′‐diphosphate (ADP), arachidonic acid (AA) and thrombin. Key findings Piplartine (100μg/ml) caused a 30% inhibition in platelet aggregation when collagen was the agonist. At 200 μg/ml, piplartine significantly inhibited the aggregation induced by arachidonic acid (100%), collagen (59%) or ADP (52%) but not that induced by thrombin. The highest concentration of piplartine (300 μg/ml) inhibited thrombin‐ (37%), ADP‐ (71%) and collagen‐ (98%) induced aggregation. The inhibitory effect of piplartine on ADP‐induced platelet aggregation was not modified by pretreatment with pentoxifylline (a phosphodiesterase inhibitor), l ‐arginine (a substrate for nitric oxide synthase) or ticlopidine (a P2Y₁₂ purinoceptor antagonist). However, aspirin, a well‐known inhibitor of cyclooxygenase, greatly increased the inhibitory effect of piplartine on arachidonic‐acid‐induced platelet aggregation. Conclusions The mechanism underlying the piplartine antiplatelet action is not totally clarified. It could be related to the inhibition of cyclooxgenase activity and a decrease in thromboxane A₂ formation, similar to that occurring with aspirin. This and other possible mechanisms require further study.     

PAF antagonism in vitro and in vivo by aglafoline from Aglaia elliptifolia Merr.

Aglafoline, isolated from Aglaia elliptifolia Merr, inhibited in a selective and concentration-dependent manner the aggregation and ATP release reaction induced in washed rabbit platelets by PAF (platelet-activating factor). The IC50 values of aglafoline, BN52021 and kadsurenone on PAF (3.6 nM)-induced platelet aggregation were about 50, 12 and 18 microM, respectively. Aglafoline also inhibited [3H]PAF (3.6 nM) binding to washed rabbit platelets with an IC50 value of 17.8 +/- 2.6 microM. The concentration-response curve of PAF-induced platelet aggregation was shifted to the right by aglafoline with pA2 and pA10 values of 5.97 and 5.04, respectively. Although thromboxane B2 formation caused by collagen and thrombin was partially suppressed by aglafoline, thromboxane B2 formation caused by ionophore A23187 and arachidonic acid was not affected. Aglafoline inhibited the [3H]inositol monophosphate formation caused by PAF but not that caused by collagen or thrombin in the presence of indomethacin (20 microM). The cAMP content of washed rabbit platelets was not affected by aglafoline. Rat femoral intravenous administration of aglafoline (10 mg/kg) did not affect blood pressure. However, aglafoline (10 mg/kg) both prophylactically and therapeutically antagonized PAF (2.5 micrograms/kg)-induced hypotensive shock in rats. Intravenous PAF (30 ng/kg) caused severe bronchoconstriction in guinea pigs. This effect was completely blocked by aglafoline. This implies aglafoline is an effective PAF antagonist not only in vitro, but also in vivo.     

Inhibition of collagen-induced platelet activation by arachidonyl trifluoromethyl ketone

Collagen-induced platelet activation is associated with, and markedly potentiated by, the release of arachidonic acid and its subsequent conversion to thromboxane A₂. The precise mechanism of arachidonic acid release is unknown. An inhibitor of isolated cytosolic phospholipase A₂ (cPLA₂), arachidonyl trifluoromethyl ketone (AACOCF₃), was used to examine the role that cPLA₂ plays in this process. AACOCF₃ inhibited platelet aggregation in response to collagen and arachidonic acid but not to thrombin, calcium ionophore, phorbol ester, or a thromboxane mimetic. Thromboxane formation stimulated by thrombin or collagen was inhibited by AACOCF₃. However, AACOCF₃ did not inhibit collagen-induced [¹⁴C]arachidonic acid release. These data are consistent with the inhibitory effects of AACOCF₃ on collagen-induced aggregation involving an action on the conversion of arachidonic acid to thromboxane.     

丁基苯酞对大鼠血栓形成及血小板功能的影响

目的研究消旋、左旋和右旋丁基苯酞(dl-,l-和d-NBP)对血栓形成及血小板功能的影响。方法利用半体外血栓形成术及比浊法,观察dl-,l-和d-NBP及阿司匹林(Asp)对大鼠血栓湿重和血小板聚集率的影响,并用放免法、荧光分光光度法测定其对血小板内cAMP和TXB2的水平以及血小板5-HT释放率的影响。结果ip,dl-NBP和l-NBP可剂量依赖性地抑制大鼠血栓形成,且l-NBP作用与Asp相似,d-NBP对半体外血栓形成无显著作用;dl-,d-和l-NBP可显著抑制胶原、ADP、花生四烯酸诱导的血小板聚集。结论NBP有抗血栓作用,l-NBP作用最强,dl-NBP作用较弱,其抗栓作用与升高血小板内cAMP的含量及抑制5-HT释放有关。     

Synthesis,Antiplatelet and Vasorelaxing Activities of Xanthone Derivatives

A series of ω‐aminoalkoxylxanthones was synthesized and tested in vitro for their ability to inhibit platelet aggregation and cause vasorelaxing action. Compounds 4 , 5 , 12 , 17 , and 18 showed significant antiplatelet effects on thrombin‐, arachidonic acid (AA)‐, collagen‐, and platelet activating factor (PAF)‐induced washed rabbit platelet aggregation and exhibited inhibition of primary and secondary aggregation induced by adenosine‐5'‐diphosphate (ADP) in human platelet‐rich‐plasma (PRP). Compounds 4 , 17 , and 18 revealed vasorelaxing activities in rat thoracic aorta. We concluded that these compounds may be developed as new antithrombotic agents.     

NP-313, 2-acetylamino-3-chloro-1,4-naphthoquinone, a novel antithrombotic agent with dual inhibition of thromboxane A(2) synthesis and calcium entry

BACKGROUND AND PURPOSE

1,4-Naphthoquinones exhibit antiplatelet activity both in vivo and in vitro. In the present study, we investigated the antiplatelet effect of a novel naphthoquinone derivative NP-313, 2-acetylamino-3-chloro-1,4-naphthoquinone and its mechanism of action.

EXPERIMENTAL APPROACH

We measured platelet aggregation, Ca²⁺ mobilization, thromboxane B2 formation and P-selectin expression and examined several enzymatic activities. Furthermore, we used the irradiated mesenteric venules in fluorescein sodium–treated mice to monitor the antithrombotic effect of NP-313 in vivo.

KEY RESULTS

NP-313 concentration-dependently inhibited human platelet aggregation induced by collagen, arachidonic acid, thapsigargin, thrombin and A23187. NP-313 also inhibited P-selectin expression, thromboxane B₂ formation and [Ca²⁺]_i elevation in platelets stimulated by thrombin and collagen. NP-313 at 10 µM inhibited cyclooxygenase, thromboxane A₂ synthase, and protein kinase Cα, whereas it did not affect phospholipase A₂ or phospholipase C activity. In the presence of indomethacin and an adenosine 5-diphosphate scavenger, NP-313 concentration-dependently inhibited thrombin- and A23187-induced [Ca²⁺]_i increase through its inhibitory effects on Ca²⁺ influx, rather than blocking Ca²⁺ release from intracellular stores. NP-313 also inhibited thapsigargin-mediated Ca²⁺ influx through store-operated calcium channel but had no effect on Ca²⁺ influx through store-independent calcium channel evoked by the diacylglycerol analogue 1-oleoyl-2-acetyl-sn-glycerol. Nevertheless, it had little effect on cyclic AMP and cyclic GMP levels. Also, intravenously administered NP-313 dose-dependently inhibited the thrombus occlusion of the irradiated mesenteric vessels of fluorescein-pretreated mice.

CONCLUSIONS AND IMPLICATIONS

Taken together, these results indicate that NP-313 exerts its antithrombotic activity through dual inhibition of thromboxane A₂ synthesis and Ca²⁺ influx through SOCC.