Antiplatelet drugs. A comparative review

Comparative efficacy and safety of Chinese patent medicines of acute ischemic stroke: A network meta-analysis

BACKGROUND

Acute ischemic stroke (AIS) is characterized by high morbidity, disability, mortality, recurrence, and economic burden. Clinical trials have demonstrated that the clinical efficacy of combining oral Chinese patent medicines (CPMs) with chemical drugs (CDs) is better than that of CDs alone. In this study, we performed a network meta-analysis (NMA) of RCTs to assess the efficacy of different CPMs in combination with CDs in the treatment of AIS.

METHODS

Search 6 databases from the beginning to January 10, 2023. The Cochrane Risk of Bias tool assessed the methodological quality of the included studies. The NMA was then performed using the STATA 13.0 program. The surface under the cumulative ranking curve (SUCRA) probability values were applied to rank the studied treatments, and cluster analysis was used to compare the effects of CPMs between 2 different outcomes.

RESULTS

A total of 94 eligible RCTs, involving 9581 participants, were included in this analysis. Nine CPMs, including Nao-mai-li granule (NML), Nao-mai-tai granule (NMT), Qi-long granule (QL), Long-sheng-zhi capsule (LSZ), Nao-xin-tong capsule (NXT), Nao-xue-shu oral liquid (NXS), Tong-xin-luo capsule (TXL), Xiao-shuan-chang-rong capsule (XSCR), and Xue-shuan-xin-mai-ning capsule (XSXMN) were included. Regarding the clinical effective rate, all types of CPMs + CDs treatments were significantly better than CDs treatments alone, with significant differences among the 9 selected CPMs. Compared with CDs, results showed that NXS + CDs performed best in improving clinical effective rate [OR = 4.73; 95% CI: 1.26-17.78; (SUCRA: 76.1%)]. TXL + CDs showed the most effective effect in alleviating National Institutes of Health Stroke Scale (NIHSS) [MD = -3.84; 95% CI: -5.23, -2.45; (SUCRA: 81.6%)]; NXT + CDs were most effective in improving Barthel index [MD = 13.05; 95% CI: 3.98-22.12; (SUCRA: 63.5%)]. Combined with other outcome indicators and the results of cluster analysis, NXS + CDs may assist in the potential optimal treatment regimen for AIS.

CONCLUSION

In conclusion, CPMs were found to be beneficial as adjuvant therapy in patients with AIS. Taking into account the clinical effective rate and other outcomes, NXS + CDs may be the most effective option to improve the condition of AIS patients.

Antiplatelet, cytotoxic activities and characterization of green-synthesized zinc oxide nanoparticles using aqueous extract of Nephrolepis exaltata

The goal of the current study was to synthesize zinc oxide nanoparticles (ZnO-NPs) using ZnCl₂.2H₂O salt precursor and an aqueous extract of Nephrolepis exaltata (N. exaltata), which act as a capping and reducing agent. N. exaltata plant extract-mediated ZnO-NPs were further characterized by various techniques, such as X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transforms infrared spectroscopy (FT-IR), UV-visible (UV-Vis), and energy-dispersive X-ray (EDX) analysis. The nanoscale crystalline phase of ZnO-NPs was analyzed by the XRD patterns. The FT-IR analysis revealed different functional groups of biomolecules involved in the reduction and stabilization of the ZnO-NPs. The light absorption and optical properties of ZnO-NPs were examined by UV-Vis spectroscopy at a wavelength of 380 nm. The spherical shape morphology of ZnO-NPs with mean particle size ranges between 60 and 80 nm was confirmed by SEM images. While the EDX analysis was used to identify the elemental composition of ZnO-NPs. Furthermore, the synthesized ZnO-NPs demonstrate potential antiplatelet activity by inhibiting the platelet aggregation induced by platelet activation factor (PAF) and arachidonic acid (AA). The results showed that synthesized ZnO-NPs were more effective in inhibiting platelet aggregation induced by AA with IC₅₀ (56% and 10 μg/mL) and PAF (63% and 10 μg/mL), respectively. However, the biocompatibility of ZnO-NPs was assessed in human lung cancer cell line (A549) under in vitro conditions. The cytotoxicity of synthesized nanoparticles revealed that cell viability decreased and the IC₅₀ was found to be 46.7% at a concentration of 75 μg/mL. The present work concluded the green synthesis of ZnO-NPs that was achieved by N. exaltata plant extract and showed good antiplatelet and cytotoxic activity, which demonstrates the lack of harmful effects making them more effective for use in pharmaceutical and medical fields to treat thrombotic disorders.

Clinical trials in long-term antiplatelet therapies: focus on the role of aspirin

PURPOSE OF REVIEW

The purpose of this review is to summarize the existing evidence for use of long-term antiplatelet therapies for primary and secondary prevention of adverse cardiovascular events.

RECENT FINDINGS

In the setting of primary prevention, several contemporary trials have shown a lack of net clinical benefit with use of aspirin across different patient groups, including those with diabetes mellitus, older age or high estimated cardiac risk. For secondary prevention, the addition of either ticagrelor or low-dose rivaroxaban to aspirin monotherapy significantly lowered recurrent vascular events, albeit with excess bleeding. Aspirin withdrawal did not result in excess thrombotic risk or less bleeding among patients undergoing percutaneous coronary intervention (PCI) treated with ticagrelor.

SUMMARY

In the contemporary era, routine use of aspirin is not beneficial in the majority of patients free of cardiac disease. In contrast, for secondary prevention, aspirin monotherapy is not sufficient to lower recurrent vascular risk. Antiplatelet monotherapy with ticagrelor may emerge as an alternative to lower bleeding whereas maintaining ischemic efficacy in selected patients undergoing PCI.

[Liposomal form of lipoic acid: preparation and determination of antiplatelet and antioxidant activity]

Optimal conditions for obtaining phosphatidylholine (PC) liposomes with lipoic acid (LA) are chosen that lead to the formation of nanoparticles with a size of 175¸284 nm with efficiency (extent) of inclusion of LA in liposomes equal 85% and characterized by a slow release of substance from the nanoparticles. The effect of "empty" liposomes and liposomal form of LA on platelet aggregation induced by arachidonic acid (AA) is established. It is found that liposomes with LА inhibit platelet aggregation, caused by AА, to 80%. In addition, it is shown that "empty" liposomes slightly (to 30%) suppress platelet aggregation, caused by AА. The amount of TBA-sensitive products in samples of platelet-rich plasma (PRP) incubated with liposomal LA is determined. It is shown that LA in the composition of liposomes retains its antioxidant properties, and the amount of products of lipid peroxidation in platelet-rich plasma decreases in a dose-dependent manner when arachidonic acid is used as an inductor of platelet aggregation. It is assumed that the antiplatelet action of the liposomal form of LА is induced by inhibition of the initiation of lipid peroxidation products caused by exogenous inducer AА. It is supposed that, after additional research, the liposomal form of LA can be considered as a new drug in complex treatment of cerebral ischemia.

Clinical, Biochemical, and Molecular Aspects of Glanzmann's Thrombasthenia in Humans and Dogs

Glanzmann's thrombasthenia (GT) is an inherited, intrinsic platelet function defect that involves the platelet glycoprotein complex IIb–IIIa, also known as the fibrinogen receptor and the integrin αIIbβ3. The defect was originally described by Dr. Glanzmann in humans in 1918 as a bleeding disorder that differed clinically from other known coagulopathies. Over the decades that followed, researchers determined the biochemical and molecular basis for the disease in humans. Otterhounds with thrombasthenic thrombopathia, described in the 1960s, were the only animal model that closely resembled the disease described in humans until 1996. At that time, a Great Pyrenees dog was identified with unequivocal clinical and biochemical features of Type I GT. The cDNA encoding for glycoproteins IIb and IIIa were sequenced in normal dogs in 1999, allowing for identification of specific mutations causing Type I GT in both Otterhounds and Great Pyrenees dogs. Knowing the molecular basis for Type I GT in dogs as well as the cDNA sequences in normal dogs should enhance the understanding of structure/function relationships of the αIIbβ3 integrin and provide an excellent animal model for studies aimed at correction of GT in humans. The following review focuses on the structure and function of this platelet receptor and reviews the molecular, biochemical, and clinical aspects of Glanzmann's thrombasthenia in humans and dogs.

Thrombosis recanalization by paeoniflorin through the upregulation of urokinase‑type plasminogen activator via the MAPK signaling pathway

Paeoniflorin, the major component of Paeonia lactiflora pall, has previously been reported to prevent thrombosis. Plasminogen activator urokinase (uPA) is a serine protease that markedly facilitates normal thrombosis resolution. Paeoniflorin and uPA have been linked to the mitogen-activated protein kinase (MAPK) signaling pathway. In the current study, the influence of paeoniflorin on the expression of uPA was investigated and the underlying regulatory mechanism was preliminarily determined. The prothrombotic state of the model animals treated with paeoniflorin were assessed by enzyme-linked immunosorbent assay (ELISA). Additionally, the cytotoxicity of paeoniflorin on human umbilical vein endothelial cell (HUVEC) cultures was estimated using a methyl thiazolyl tetrazolium assay and the possible pathways involved in the interaction between paeoniflorin and uPA were evaluated using western blot analysis. The ELISA results demonstrated that the levels of 6-keto prostaglandin F_1a, fibronectin and uPA were significantly upregulated by treatment with paeoniflorin compared with control (P<0.05). By contrast, the expression of fibrinogen, D-dimer and thromboxane B₂ were inhibited. With an increase in the concentration of paeoniflorin the cell viability of HUVECs decreased gradually. The results of western blot analysis demonstrated that paeoniflorin increased the phosphorylation of MAPK 14 (p38) and MAPK 8 (JNK). The present study demonstrated that paeoniflorin has the potential to improve the prethrombotic state and recanalize thrombosis by increasing the expression of uPA, which may be mediated via regulation of the p38 and JNK MAPK signaling pathways. However, this treatment effect was dependent on the concentration of paeoniflorin used, an unsuitable concentration of the agent would result in a negative effect on the anti-thrombosis pathways.

Paeonol enhances thrombus recanalization by inducing vascular endothelial growth factor 165 via ERK1/2 MAPK signaling pathway

Paeonol (2'-hydroxy-4'-methoxyacetophenone) is the major active compound of Mautan cortex and has been demonstrated to inhibit platelet aggregation in previous studies. The current study aimed to elucidate the underlying molecular mechanism of paeonol in recanalizing thrombi. The presence of indicators of prothrombotic state (PTS) in the serum of the model animals were determined by enzyme‑linked immunosorbent assay (ELISA) assay and the cytotoxicity of paeonol on human umbilical vein endothelial cell (HUVEC) cultures was estimated by 3‑(4,5 dimethylthiazol‑2‑yl)-2,5-diphenyltetrazolium bromide assay. The possible underlying signaling pathway involved in the interaction between paeonol and vascular endothelial growth factor 165 (VEGF165) was investigated using western blotting. The levels of 6‑keto‑prostaglandin F1α, fibronectin, and VEGF165 in serum were significantly upregulated by the treatment of paeonol while the levels of fibrinogen, D‑dimer, and thromboxane B2 were significantly downregulated (P<0.05). With increased paeonol concentration, the cell viability of HUVECs gradually decreased. The results of the western blot analysis demonstrated that paeonol increased the expression levels of phosphorylated‑extracellular signal‑regulated kinase (ERK1/2) and VEGF165 but had no marked effect on the expression level of ERK1/2. Paeonol has the potential to improve PTS and recanalize thrombi in animal models, which may be by the upregulation of VEGF165 via the ERK1/2 mitogen activated protein kinase signaling pathway. However, this positive effect depended on the concentration of paeonol used, an unsuitably high concentration of the compound exerted negative effects on the anti‑thrombosis signaling pathways.

Synthesis and biological evaluation of some dibenzofuran-piperazine derivatives

In the present paper, a novel series of dibenzofuran-piperazine derivatives were synthesized via the treatment of N-(2-methoxy-3-dibenzofuranyl)-2-chloroacetamide with substituted piperazine derivatives. The chemical structures of the compounds were elucidated by (1)H NMR, (13)C NMR, mass spectral data; elemental analysis and HPLC analysis. Each derivative was evaluated for antiplatelet activity and anticholinesterase activity. Compound 2 m with 2-furoyl moiety exhibited high percentage inhibition as much as standard drug aspirin on arachidonic acid (AA)-induced platelet aggregation. None of the compounds presented significant inhibitor effect on collagen-induced platelet aggregation. Furthermore, the anticholinesterase activity of the compounds was determined and they did not show promising inhibitor activity compared with standard drug donepezil.

Mechanism of endothelial cyto-protective and thrombo-resistance effects of sildenafil, vardenafil and tadalafil in male rabbit

INTRODUCTION

PDE5 inhibitors (PDE5inhs) have proven to be of great impact in the treatment of numerous human extra-sexual diseases and their chronic use may induce endothelial rehabilitation. This study aimed to assess the effects of PDE5inhs at chronic administration to explore the possible endothelial cyto-protective and thrombo-resistance effects.

MATERIAL AND METHODS

One hundred New Zealand white male rabbits were divided into four groups. The first group (control, C) received 1 ml saline/kg, the second group (S) received 10 mg/kg sildenafil, the third group (V) received 2 mg/kg vardenafil, and the fourth group (T) received 2 mg/kg tadalafil in saline I.P. three times weekly for 4 weeks. Blood samples were collected and plasma was isolated for determination of 2,3-dinor-6-keto-prostaglandin F-1α (PGF1α), 11-dehydro-TXB2 (TXB2), fibrinogen, calcium levels, prothrombin (PT), and thrombin times (TT).

RESULTS

PDE5inhs significantly increase PGF1α, calcium levels, PT and TT (p < 0.001) when compared with baseline data or with the saline group at the end of treatment. In contrast, PDE5inhs significantly decrease TXB2 and fibrinogen levels (p < 0.001) when compared either with their baseline data or with the saline group at the end of treatment. The tadalafil group showed a lower increase in PGF1α (p < 0.001), lower decrease in TXB2 (p < 0.001), and higher increase in calcium levels (p < 0.01, p < 0.05), lower increase in PT and TT levels (p < 0.001) when compared with sildenafil or vardenafil.

CONCLUSIONS

The prolonged use of PDE5inhs has time-dependent mild to moderate endothelial cyto-protective, thrombo-resistance anti-inflammatory and anti-nociception effects via activation of endothelial NOS (eNOS), increase of PGI2 synthesis and decrease of fibrinogen with significant increase in PT and TT.

A peripherally restricted P2Y12 receptor antagonist altered rat tumor incidences with no human relevance: Mode of action consistent with dopamine agonism

Background

Ticagrelor is an orally available, direct acting and reversible P2Y₁₂ receptor antagonist approved for treatment of acute coronary syndrome. The objectives of these studies were to (1) evaluate the Ticagrelor 2-year rat carcinogenicity bioassay data; (2) investigate potential mode of action (MOA) and (3) interpret human relevance.

Methods

The following studies were done (1) rat two-year carcinogenicity study in male and female rats, (2) in vitro and in vivo genotoxicity assays, (3) quantitative whole body autoradiography (QWBA; male and female rats), (4) in vitro pharmacological profiling for more than 300 assays, and (5) in vivo ovariectomized rat assay.

Results

The carcinogenicity study indicated Ticagrelor increased uterine tumor incidence while decreasing mammary and pituitary tumors/hyperplasia incidences in only high dose female rats. However, this altered tumor incidences were not P2Y₁₂ target related since marketed non-reversible P2Y₁₂ receptor antagonists were not associated with alter tumor incidences. MOA studies determined Ticagrelor exposure in the anterior pituitary and Ticagrelor was (1) non-genotoxic, (2) peripherally-restricted, (3) a dopamine transport (DAT) inhibitor with an IC₅₀ lower than systemic free exposure in the rat carcinogenic study and more than a log higher than the free systemic exposure seen in clinical trials and (4) an inhibitor of estradiol-induced prolactin secretion.

Discussion

Similar to Ticagrelor, centrally active dopamine agonists induce the same altered tumor incidence patterns that according to literature do not translate into the clinical setting, with a MOA involving decreased prolactin secretion. The Ticagrelor MOA data and literature suggest that altered dopamine levels in the hypophyseal part of the hypothalamus–hypophyseal axis (by Ticagrelor) will result in similar altered tumor incidences in rat that do not translate into the clinical setting, based on qualitative species differences. In conclusion Ticagrelor increased uterine tumors in the rat carcinogenesis study by a MOA consistent with reduced dopamine inhibition of prolactin, which is not a patient safety risk.

Synthesis and Caco-2 cell permeability of N-substituted anthranilamide esters as ADP inhibitor in platelets

Twelve N-substituted anthranilamide esters (1-5, 8, 9, 12, 13, and 15-17) were synthesized and evaluated for their ability to inhibit the in vitro aggregation by washed human platelets induced by adenosine 5'-diphosphate (10 μM). The antiplatelet activity of DL-n-butyl 5-hydroxy-N-(2-phenoxypropionyl)anthranilate (9, IC50 = 10.5 μM) was most active among the tested compounds and ethyl ester 8 (IC50 = 11.2 μM) showed the second most activity. DL-Ethyl and DL-n-butyl 5-(p-toluenesulfonyloxy)-N-(2-phenoxypropionyl)anthranilate (12, IC50 = 13.1 μM and 13, IC50 = 14.0 μM), DL-methyl N-(2-phenoxybutyryl)anthranilate (2, IC50 = 12.7 μM), DL-N-(2-phenoxypropionyl)anthranilic acid (5, IC50 = 13.7 μM) displayed lower antiplatelet activity than 8 and 9. Compound 5 was more active than methyl ester prodrug 1. n-Butyl 5-hydroxy-N-(4'-acetoxybenzoyl)anthranilate (15, IC50 = 28.3 μM) showed moderate activity. Compounds 1 (IC50 = 42.8 μM), 4 (IC50 = 56.7 μM), 16 (IC50 = 51.0 μM), and 17 (IC50 = 49.8 μM) exhibited low antiplatelet activity. Methyl N-phenoxyacetylanthranilate (3, IC50 = 78.0 μM) showed the lowest antiplatelet activity. The compounds with branched alkyl chain (2 and 5) were more active than compounds with straight chain (3 and 4). The apparent permeability coefficient (Papp, cm/s) values of compounds 2 and 9 were determined as 45.34 ± 4.67 and 33.17 ± 5.15 × 10(-6) cm/s by Caco-2 cell permeability assay.

Bioequivalence and tolerability study of two brands of clopidogrel tablets, using inhibition of platelet aggregation and pharmacodynamic measures

BACKGROUND

The role of platelets in acute cardiovascular atherothrombotic events has been well established and attention has focused on platelet inhibition therapy. Clopidogrel is a novel thienopyridine inhibitor of adenosine diphosphate-induced platelet activation. Recent studies have shown that in the setting of coronary angioplasty/stenting, a loading dose of 300 mg followed by 75 mg once daily is required for optimum benefit.

OBJECTIVE

This study assessed the bioequivalence and tolerability of 2 oral formulations of clopidogrel 75-mg tablets.

METHODS

This 10-day, open-label, randomized, parallel-group, comparative bioequivalence and tolerability study was carried out in the Department of Clinical Pharmacology and Therapeutics, Nizam's Institute of Medical Sciences (Hyderabad, India). Young healthy male volunteers were enrolled. Subjects were randomized to receive one of two 75-mg tablet formulations of clopidogrel (Clopivas(®) [test formulation] or Plavix(®) [reference formulation]). Subjects first received a 300-mg loading dose (four 75-mg tablets) on day 1, followed by 75 mg (1 tablet) at 8:00 AM daily for the next 6 days. Inhibition of platelet aggregation, which is the pharmacologic basis for the therapeutic efficacy of antiplatelet agents, and the effect on bleeding time were used as the pharmacodynamic assessment criteria. Pharmacodynamic variables included mean of maximum activity of percentage of inhibition of platelet aggregation (Emax), mean time to reach Emax (tmax), and mean area under the activity-time curve from time 0 to 168 hours (AUC0-168). Tolerability assessments included blood pressure and heart rate measurements before and at regular intervals (every hour for 12 hours and then at 24 hours) over a 24-hour period after drug administration. Clinical tolerability was assessed using adverse effects, platelet count (assessed on days 3, 6, and 10 after first-dose administration), and neutrophil count (assessed on day 10 after first-dose administration).

RESULTS

Twenty subjects were enrolled (mean [SD] age, 26.5 [2.9] years [range, 22-32 years]). Emax, tmax, and AUC0-168 were similar between the 2 groups, as was bleeding time. The 90% CIs were within the bioequivalence acceptance range of 80% to 125%. One subject (10%) in the Plavix group experienced mild headache; no serious adverse effects were reported, and none of the subjects dropped out due to an adverse effect. Platelet and neutrophil counts were found to be within normal limits.

CONCLUSIONS

In this study of healthy male volunteers, the 2 tablet preparations of clopidogrel showed bioequivalence. However, the sample size was smaller than that generally recommended for a bioequivalence study, and additional studies with larger sample sizes are needed.

Lignans from the aerial parts of Saururus chinensis: isolation, structural characterization, and their effects on platelet aggregation

Five new diaryldimethylbutane lignans, saurulignans A-E (1-5), four new tetrahydrofuran lignans, saurufurins A-D (6-9), and one arylnaphthalene lignan, saurunarin (10), were isolated from Saururus chinensis, along with 18 known compounds. Lignan 5 showed significant inhibition of ADP-induced aggregation with an IC50 value of 9.8 μM and AA-induced aggregation with an IC50 value of 14.0 μM. Compound 19 showed significant activity to inhibit PAF-induced aggregation with an IC50 value of 9.1 μM. In addition, five isolated compounds could induce platelet aggregation. These results suggest that secondary metabolites in S. chinensis have bidirectional regulation on blood clotting and anticlotting effects.

The role of 3-hydroxy-3-methylglutaryl coenzyme a reductase inhibitors (statins) in modern rheumatology

Inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase commonly known as statins are widely used for treating hypercholesterolemia. However, there is much evidence to suggest that statins may have other properties in addition to their cholesterol-lowering effect. In particular, statins may neutralize post-translational prenylation of vitally important regulatory small GTPases, which are involved in several processes such as tissue fibrosis, cell maturation, apoptosis, immune cell maturation, and immune response. The beneficial effect of statins has been reported in animal and in vitro models as well as in some clinical studies. As they have an acceptable safety profile, statins may be considered, in selected cases, as a valuable concomitant therapy in the treatment of rheumatic and autoimmune disorders.

Disposition and metabolism of ticagrelor, a novel P2Y12 receptor antagonist, in mice, rats, and marmosets

Ticagrelor is a reversibly binding and selective oral P2Y(12) antagonist, developed for the prevention of atherothrombotic events in patients with acute coronary syndromes. The disposition and metabolism of [(14)C]ticagrelor was investigated in mice, rats, and marmosets to demonstrate that these preclinical toxicity species showed similar metabolic profiles to human. Incubations with hepatocytes or microsomes from multiple species were also studied to compare with in vivo metabolic profiles. The routes of excretion were similar for both oral and intravenous administration in mice, rats, and marmosets with fecal excretion being the major elimination pathway accounting for 59 to 96% of the total radioactivity administered. Urinary excretion of drug-related material accounted for only 1 to 15% of the total radioactivity administered. Milk samples from lactating rats displayed significantly higher levels of total radioactivity than plasma after oral administration of ticagrelor. This demonstrated that ticagrelor and/or its metabolites were readily transferred into rat milk and that neonatal rats could be exposed to ticagrelor-related compounds via maternal milk. Ticagrelor and active metabolite AR-C124910 (loss of hydroxyethyl side chain) were the major components in plasma from all species studied and similar to human plasma profiles. The primary metabolite of ticagrelor excreted in urine across all species was an inactive metabolite, AR-C133913 (loss of difluorophenylcyclopropyl group). Ticagrelor, AR-C124910, and AR-C133913 were the major components found in feces from the three species examined. Overall, in vivo metabolite profiles were qualitatively similar across all species and consistent with in vitro results.

Efficacy and safety of abciximab in diabetic patients who underwent percutaneous coronary intervention with thienopyridines loading: a meta-analysis

BACKGROUND

It has been controversial whether abciximab offered additional benefits for diabetic patients who underwent percutaneous coronary intervention (PCI) with thienopyridines loading.

METHODS

MEDLINE, EMBASE, the Cochrane library clinical trials registry, ISI Science Citation Index, ISI Web of Knowledge and China National Knowledge Infrastructure (CNKI) were searched, supplemented with manual-screening for relevant publications. Quantitative meta-analyses were performed to assess differences between abciximab groups and controls with respect to post-PCI risk of major cardiac events (MACEs), angiographic restenosis and bleeding complications.

RESULTS

9 trials were identified, involving 2,607 diabetic patients receiving PCI for coronary artery diseases. Among those patients who underwent elective PCI or primary PCI, pooling results showed that abciximab did not significantly reduce risks of MACEs (for elective-PCI patients: RR(1-month): 0.93, 95% CI: 0.60-1.44; RR(1-year): 0.95, 95% CI: 0.81-1.11; for primary-PCI patients: RR(1-month): 1.05, 95% CI: 0.70-1.57; RR(1-year): 0.98, 95% CI: 0.80-1.21), nor all-cause mortality, re-infarction and angiographic restenosis in either group. The only beneficial effect by abciximab appeared to be a decrease 1-year TLR (target lesion revascularization) risk in elective-PCI patients (RR1-year: 0.83, 95% CI: 0.70-0.99). Moreover, occurrence of minor bleeding complications increased in elective-PCI patients treated with abciximab (RR: 2.94, 95% CI: 1.68-5.13, P<0.001), whereas major bleedings rate was similar (RR: 0.83, 95% CI: 0.27-2.57).

CONCLUSIONS

Concomitant dosing of abciximab and thienopyridines provides no additional benefit among diabetic patients who underwent PCI; this conclusion, though, needs further confirmation in larger studies.

Antiplatelet effects of Spatholobus suberectus via inhibition of the glycoprotein IIb/IIIa receptor

ETHNOPHARMACOLOGICAL RELEVANCE

The vine stem of Spatholobus suberectus is a widely used blood-activating and stasis-dispelling medicine for the treatment of diseases related to blood stasis syndrome in traditional medicine in Korea, Japan, and China.

AIM OF THE STUDY

To demonstrate the clinical effects of Spatholobus suberectus against blood stasis syndromes using in vitro and in vivo platelet aggregation studies and to investigate its exact mechanisms.

MATERIALS AND METHODS

We extracted vine stems of Spatholobus suberectus, using 95% EtOH (SSE) and investigated its antiplatelet activity on platelet aggregation induced by collagen and ADP in human platelet-rich plasma (PRP). For the mechanism study, a glycoprotein IIb/IIIa (GP IIb/IIIa) assay using flow cytometric analysis and a thromboxane A(2) (TXA(2)) assay were performed. In addition, we investigated the effects of SSE in a thromboembolic mouse model.

RESULTS

SSE significantly inhibited ADP- and collagen-induced platelet aggregation in human PRP concentration-dependently without affecting plasma clotting time. It also significantly inhibited fibrinogen binding to the GP IIb/IIIa receptor and partly inhibited the formation of TXA(2). In the in vivo study, oral administration of SSE dose-dependently suppressed the death of thromboembolism model mice induced by intravenous injection of collagen plus epinephrine.

CONCLUSIONS

SSE showed antiplatelet activity without anticoagulant effects mainly through the inhibition of fibrinogen binding to the GP IIb/IIIa receptor. Our current results support the clinical usage of SSE in the East Asian region treating atherothrombotic diseases and may represent a new natural source to develop antiplatelet agents.

Effects of kiwi fruit consumption on platelet aggregation and plasma lipids in healthy human volunteers

Fruits and vegetables have been thought to be beneficial in cardiovascular disease. The beneficial effects of fruits and vegetables may be explained by the antioxidants and other components contained therein. These nutrients may function individually or in concert to protect lipoproteins and vascular cells from oxidation, or by other mechanisms such as reducing plasma lipid levels (LDL cholesterol, triglycerides), and platelet aggregation response. Kiwi fruit which contains high amounts of vitamin C, vitamin E and polyphenols may be beneficial in cardiovascular disease; however very little is known about its cardioprotective effects. Platelets are involved in atherosclerotic disease development and the reduction of platelet activity by medications reduces the incidence and severity of disease. To this end, we evaluated whether consuming kiwi fruit modulated platelet activity and plasma lipids in human volunteers in a randomized cross-over study. We report that consuming two or three kiwi fruit per day for 28 days reduced platelet aggregation response to collagen and ADP by 18% compared with the controls (P < 0.05). In addition, consumption of kiwi fruit lowered blood triglycerides levels by 15% compared with control (P < 0.05), whereas no such effects were observed in the case of cholesterol levels. All these data indicate that consuming kiwi fruit may be beneficial in cardiovascular disease.

Inhibitory effect of aqueous extracts of some herbs on human platelet aggregation in vitro

Effect of aqueous extract of several herbs on human platelet aggregation in vitro was investigated. Out of 28 herbs/nutriceuticals investigated, camomile, nettle alfalfa, garlic and onion exhibited most significant anti-platelet activity (>or=45% inhibition). Aqueous extracts of alfalfa, fresh nettle, and camomile inhibited ADP induced-platelet aggregation by 73, 65 and 60%, respectively, compared with control (P < 0.05). Camomile and alfalfa inhibited collagen-induced platelet aggregation by 84 and 65%, respectively, but nettle could not inhibit collagen-induced aggregation. In contrast, nettle was the most potent inhibitor (66%) of whole blood aggregation induced by collagen, followed by alfalfa (52%), and camomile (30%) compared with control (P < 0.05). None of these three herbs however could inhibit arachidonic acid or thrombin induced platelet aggregation. Camomile and alfalfa strongly inhibited thromboxane B2 synthesis induced by ADP or collagen, but nettle had no effect. Alfalfa and nettle increased cGMP levels in platelets by 50 and 35%, respectively, compared with the control (1.85 +/- 0.23 nM) (P < 0.005). All these data indicate that camomile, nettle and alfalfa have potent anti-platelet properties, and their inhibitory actions are mediated via different mechanisms.

Aspirin esterase activity - Evidence for skewed distribution in healthy volunteers

BACKGROUND

Aspirin, with its analgesic, anti-inflammatory, antipyretic, and anti-platelet actions, is one of the most frequently used drugs. Although its use as prophylaxis against thromboembolism is well established, an optimal dose, conferring maximal anti-platelet action without increased risk of bleeding, remains elusive.

METHOD

We assessed the possible pharmacokinetic contribution to this problem in 107 healthy, non-medicated volunteers. Serum aspirin esterase activity was evaluated at 37 degrees C with 1 mM aspirin as substrate. On the basis of the report that most of aspirin esterase activity is accounted for by pseudocholinesterase, we additionally quantified the activity of this enzyme, with and without dibucaine as an inhibitor, using Ellman's reaction, in 41 of our volunteers.

RESULTS

Aspirin esterase activities in all of our volunteers (33.90 nmol/ml/min to 222.65 nmol/ml/min, median 103.45 nmol/ml/min) showed a continuous and skewed distribution with eight outliers. In the 41 subjects so studied, aspirin esterase activities correlated positively with both pseudocholinesterase activities (Spearman's rho=0.593, p<0.001) and dibucaine numbers (Spearman's rho=0.422, p<0.01).

CONCLUSIONS

Our results support previous observations that the rate of aspirin hydrolysis is not determined by aspirin esterase alone and that other factors are probably involved. Additionally, the skewed distribution of aspirin esterase activities makes a case for its possible contribution to the phenomenon of aspirin resistance.

Optimal antiplatelet treatment for percutaneous coronary intervention: Clopidogrel vs. ticlopidine

Antiplatelet treatment for patients undergoing percutaneous coronary interventions is a rapidly changing area. Thienopyridines derivatives (ticlopidine and clopidogrel) have shown to decrease major cardiovascular events. Ticlopidine can cause rare but serious side effects, especially during the first 3 months of treatment. Clopidogrel appears to be a safer alternative to ticlopidine. However, resistance to clopidogrel therapy may increases the risk of recurrent cardiovascular events. Whether increased doses of clopidogrel might overcome this resistance in nonresponsive patients warrants further investigation.

Design of a transdermal delivery system for aspirin as an antithrombotic drug

Aspirin has become the gold standard to which newer antiplatelet drugs are compared for reducing risks of cardiovascular diseases, while keeping low cost. Oral aspirin has a repertoire of gastrointestinal side effects even at low doses and requires high frequent dosing because it undergoes extensive presystemic metabolism. Transdermal delivery offers an alternative route that bypasses the gut and may be more convenient and safer for aspirin delivery especially during long-term use. This study comprised formulation of aspirin in different topical bases. Release studies revealed that hydrocarbon gel allowed highest drug release. In vitro permeation studies revealed high drug permeation from hydrocarbon gel. Several chemical penetration enhancers were monitored for augmenting the permeation from this base. Combination of propylene glycol and alcohol showed maximum enhancing effect and, hence, was selected for biological investigation. The biological performance of the selected formulation was assessed by measuring the inhibition of platelet aggregation relevant to different dosage regimens aiming to minimize both drug dose and frequency of application. The results demonstrated the feasibility of successfully influencing platelet function and revealed that the drug therapeutic efficacy in transdermal delivery system is dose independent. Biological performance was re-assessed after storage and the results revealed stability and persistent therapeutic efficacy.

The 5-hydroxytryptamine2A receptor antagonist sarpogrelate hydrochloride inhibits acute platelet aggregation in injured endothelium

In this study, the effect of sarpogrelate hydrochloride, a 5-hydroxytryptamine2A receptor antagonist, on platelet aggregation at the site of injured carotid artery endothelium was examined. The rat common carotid artery was clamped for 30 min to induce endothelial injury. Sarpogrelate hydrochloride was administered before and after the injury, and the effects were compared with those in rats receiving sham operation only and those receiving clipping injury but no sarpogrelate hydrochloride. The animals were killed 24 h after the procedure. The common carotid artery was examined by scanning electron microscopy and stained immunochemically for factor VIII. Sarpogrelate hydrochloride treatment was associated with reduced aggregation of platelets on electron microscopy and lower expression of factor VIII at the injured intima. Sarpogrelate hydrochloride has an inhibitory effect on platelet aggregation at the intima in the acute stage after injury, suggesting that this drug may be used to prevent early ischaemic complications after surgical or endovascular arterial intervention.

Synthesis and evaluation of antiplatelet activity of trihydroxychalcone derivatives

In an effort to develop potent antiplatelet agents, a series of trihydroxychalcones was synthesized and screened in vitro for their inhibitory effects on washed rabbit platelet aggregation induced by arachidonic acid (100 microM) and collagen (10 microg/ml). Of five compounds with potent inhibitory effects on arachidonic acid- and collagen-induced platelet aggregation, compound 4e was found to be the most potent. The structure-activity relationships suggested that antiplatelet activity was governed to a greater extent by the substituent on B ring of the chalcone template, and most of the active compounds had methoxy or dimethoxy groups on B ring.

Structural insights in platelet receptor synergism-antiplatelet therapy in post-ischemic cerebrovascular events

Synergy between agonists of platelet aggregation, namely, ADP and epinephrine, has been studied in patients having a history of cerebrovascular ischemic event. There is a significant variability of responsiveness among individuals towards clopidogrel, which is a specific inhibitor of the low-affinity human purinergic receptor (P2Y12). For responders of clopidogrel, simultaneous application of ADP and epinephrine at sub-threshold concentrations (i.e., concentration below the threshold concentration at which aggregation occurs) leads to platelet aggregation, which is followed by deaggregation. For non-responders of the drug, the synergism seems to be stronger, showing no deaggregatory pattern. The inhibition of synergism by yohimbine hydrochloride (YH), a blocker of alpha2A-adrenoreceptors is more pronounced in non-responders. A simple structural model based on receptor-receptor interaction is proposed to explain the synergism. The model explains synergy in terms of cooperative interaction between the low-affinity ADP receptor P2Y12 (Swiss Prot:Q9H244) and the alpha2A-adrenoreceptor (Swiss Prot:P08913). It follows that the synergistic effect can be achieved in only one of the two 3D structures for the alpha2A-adrenoreceptor P08913 permitted by homology modeling, as there is a better docking interface with the Q9H244. The synergism itself and the observed dichotomous phenomenon in relation to inhibition of synergism among responders and non-responders can be accounted for, if the interacting receptors on the dynamic membrane interface compete with the clopidogrel binding.

Map-ISODATA demarcates regional response to combination rt-PA and 7E3 F(ab')2 treatment of embolic stroke in the rat

PURPOSE

To investigate the ability of map-ISODATA (Iterative Self-Organizing Data Analysis Technique) to classify the different categories of ischemic damage in the lesion and to evaluate a combined (thrombolysis plus antiplatelet) treatment efficacy in an embolic stroke of rat.

MATERIALS AND METHODS

Rats subjected to embolic stroke with (N=12) and without (N=10) rt-PA and 7E3 F(ab')2 treatment (4 hours after embolization) were followed (at 2, 24, and 48 hours post-MCAO) with magnetic resonance imaging (MRI) using T1, T2, and apparent diffusion coefficient of water (ADCw). ISODATA was computed from T1, T2, and ADCw maps. The signatures characterized by the map-ISODATA were compared with histological quantitative evaluation and were employed to demarcate the specific regions in the lesion.

RESULTS

The signature described by map-ISODATA is highly correlated with the degree of tissue damage in the lesion and can distinguish the severity of ischemic tissue injury. Based upon map-ISODATA, ischemic lesion area can be divided into three specific regions, each characterized by a distinct evolution of injury and treatment response. The combined treatment significantly reduces the lesion size between 24 and 48 hours and improves the outcome 48 hours post-MCAO compared with the control group.

CONCLUSION

Map-ISODATA provides an accurate means to identify lesion area, to distinguish ischemic damage, and to detect treatment response. 7E3 F(ab')2 extends the rt-PA treatment window to at least four hours after the onset of embolic stroke of rat.

Place of drug therapy in the treatment of carotid stenosis

Carotid stenosis is an important cause of transient ischaemic attacks and stroke. The cause of carotid stenosis is most often atherosclerosis; contributing to the pathogenesis of the lesion are endothelial injury, inflammation, lipid deposition, plaque formation, fibrin, platelets and thrombin. Carotid stenosis accounts for 10-20% of cases of brain infarction, depending on the population studied. Despite successful treatment of selected patients who have had an acute ischaemic stroke with tissue plasminogen activator and the promise of other experimental therapies, prevention remains the best approach to reducing the impact of ischaemic stroke. High-risk or stroke-prone patients can be identified and targeted for specific interventions. At this juncture, treatment of carotid stenosis is a well established therapeutic target and a pillar of stroke prevention. There are two main strategies for the treatment of carotid stenosis. The first approach is to stabilise or halt the progression of the carotid plaque through risk factor modification and medication. Hypertension, diabetes mellitus, smoking, obesity and high cholesterol levels are closely associated with carotid stenosis and stroke; control of these factors may decrease the risk of plaque formation and progression. The second approach is to eliminate or reduce carotid stenosis through carotid endarterectomy or carotid angioplasty and stenting. Carotid endarterectomy, which is the mainstay of therapy for severe carotid stenosis, is beyond the scope of this review. Anticoagulants seem to play little role (if any) in the medical (i.e. non-surgical) treatment of carotid stenosis. Adoption of a healthy lifestyle combined with the reduction of risk factors has been shown to lead to a reduction in the extent of carotid stenosis. The medical treatment of carotid stenosis should be based on the triad of the reduction of risk factors, patient education, and use of antiplatelet agents.

Use of Antiplatelet Drugs in the Stroke Unit of a Hong Kong Hospital

OBJECTIVE

Antiplatelet drugs are widely used for secondary prevention of thrombotic cerebrovascular disease. The antiplatelet prescribing patterns has been evaluated in several studies but data about Hong Kong patients are lacking. This study is to investigate the prescribing patterns of antiplatelet agents in a Hong Kong hospital.

METHOD

All patients over 18 years, who attended the stroke unit between 1 October 2002 and 31 December 2002 and were on antiplatelet therapy were included in the study. Data were collected through retrospective chart review and recorded on a standardized data collection form. Continuous and categorical data were expressed as mean and counts respectively. Factors that determine frequency and pattern of antiplatelet therapy were assessed in multiple logistic regression models.

RESULTS

Three hundred and nineteen patients were included in the study. Aspirin and clopidogrel accounted for 82.1 and 16.3 of all prescriptions respectively and remaining patients were on aspirin/dipyridamole. Patients with no history of aspirin use were less likely to be treated with clopidogrel compared with those experienced aspirin intolerance (OR=0.004, 95 CI 0.000-0.051). Patients with history of gastrointestinal (GI) diseases were more likely to receive clopidogrel than those had no history of GI disorders (OR=154.86, 95 CI 33.76-710.38). Atrial fibrillation (AF) was positively associated with clopidogrel prescription (OR=11.83, 95 CI 1.21-115.85). In addition, patients with concomitant gastroprotective drugs received clopidogrel significantly less often than those without gastroprotective agents (OR=0.06, 95 CI 0.01-0.29).

CONCLUSION

Use of antiplatelet agents in patients receiving antiplatelet therapy of the stroke unit has complied with existing evidences. Several factors that determine choice between aspirin and clopidogrel were identified which included history of aspirin use and GI disorders, AF and co-prescribed gastroprotective drugs.

Pharmacokinetics and pharmacodynamics of terbogrel, a combined thromboxane A2 receptor and synthase inhibitor, in healthy subjects

AIMS

To characterize the pharmacokinetics of terbogrel, a new combined thromboxane A2 (TxA2) receptor and synthase inhibitor, in healthy human subjects after single or multiple oral administration.

METHODS

Forty-eight healthy male subjects received a single oral dose (10, 25, 50, 100, 150 or 200 mg) of terbogrel or placebo and 32 different subjects received one of the following treatments twice daily for 7 days: 50, 100 or 150 mg terbogrel, placebo, or once-a-day 330 mg acetylsalicylic acid.

RESULTS

Terbogrel was well tolerated without obvious adverse effects following either a single oral dose or administration over 7 days. Plasma drug concentrations were dose-linear and there was no accumulation over 7 days. There was a dose-dependent blockade of TxA2 receptors and of inhibition of thromboxane synthase activity with values for IC50 of 12 ng ml(-1) and 6.7 ng ml(-1), respectively. At the highest dose tested (150 mg) there was almost complete inhibition of thomboxane synthase and thromboxane receptor occupancy. Even at trough concentrations, receptor occupancy remained above 80% and thromboxane synthase was still completely inhibited. These two activities were associated with a dose-dependent inhibition of platelet aggregation (>80% at the 150 mg dose of terbogrel) and enhanced prostacyclin production.

CONCLUSIONS

Terbogrel is a potent agent having two distinct, complimentary pharmacodynamic actions, namely inhibition of thromboxane synthase and antagonism of the TxA2 receptor. The antithrombotic effect of terbogrel was dose-dependent and was associated with enhanced prostacyclin production. Terbogrel is an attractive candidate for long-term antithrombotic therapy.

Antiplatelet and Antithrombin Therapy for Early Management of Acute Coronary Syndromes

Acute coronary syndromes (ACS) are defined as either unstable angina (UA), non-ST-segment elevation myocardial infarction (NSTEMI), or ST-segment elevation myocardial infarction (STEMI). Their management is continuously evolving in terms of pharmacologic therapy. The usual cause of ACS is the disruption of an atherosclerotic plaque leading to formation of a thrombus within a coronary artery. Initial antiplatelet and antithrombin therapy for patients with ST-segment elevation (STE) ACS includes aspirin and unfractionated heparin (UFH). Patients presenting to the hospital early may undergo percutaneous intervention (PCI) with administration of additional medications such as clopidogrel and abciximab or may receive a fibrinolytic agent. Patients with non-ST-segment elevation (NSTE) ACS receive aspirin, clopidogrel, either a low-molecular-weight heparin or UFH, and, in selected patients, a glycoprotein (GP) IIb/IIIa receptor blocker. All of these agents have shown benefit when administered to patients with ACS, but results vary depending on the type of syndrome, timing of administration, and patient’s overall risk. Their mechanism of action, role in ACS, clinical practice recommendations, adverse effects, and monitoring are reviewed. Some inherent limitations to agents such as aspirin and UFH require the need for newer treatment approaches. Therefore, newer classes of drugs such as the direct thrombin inhibitor bivalirudin and the selective factor Xa inhibitor fondaparinux are being explored as alternatives to heparins for ACS management.

Platelet ADP receptor antagonists: ticlopidine and clopidogrel

The central role of platelets in the pathophysiology of arterial vascular disease has focused attention on the development of effective platelet inhibitor modalities to mitigate the clinical consequences of atherothrombotic disease. Aspirin has been the gold standard of therapy and is effective in cerebral, coronary and peripheral arterial disease with a 25% reduction in myocardial infarction, stroke and vascular death. The platelet ADP receptor antagonists were developed to further improve the clinical results of therapy. Ticlopidine provides an additional 10% relative risk reduction over aspirin alone in stroke prevention and coronary stent placement. However, ticlopidine is accompanied by occasional life-threatening adverse hematological events. The action of clopidogrel is similar to that of ticlopidine, and it is comparably effective. However, the side-effect profile of clopidogrel is much more favorable.