Glycoprotein IIb/IIIa inhibitors: an update on the mechanism of action and use of functional testing methods to assess antiplatelet efficacy

An Updated Review on Glycoprotein IIb/IIIa Inhibitors as Antiplatelet Agents: Basic and Clinical Perspectives

The glycoprotein (GP) IIb/IIIa receptor is found integrin present in platelet aggregations. GP IIb/IIIa antagonists interfere with platelet cross-linking and platelet-derived thrombus formation through the competition with fibrinogen and von Willebrand factor. Currently, three parenteral GP IIb/IIIa competitors (tirofiban, eptifibatide, and abciximab) are approved for clinical use in patients affected by percutaneous coronary interventions (PCI) in the location of acute coronary syndrome (ACS). GP IIb/IIIa antagonists have their mechanism of action in platelet aggregation prevention, distal thromboembolism, and thrombus formation, whereas the initial platelet binding to damage vascular areas is preserved. This work is aimed to provide a comprehensive review of the significance of GP IIb/IIIa inhibitors as a sort of antiplatelet agent. Their mechanism of action is based on factors that affect their efficacy. On the other hand, drugs that inhibit GP IIb/IIIa already approved by the FDA were reviewed in detail. Results from major clinical trials and regulatory practices and guidelines to deal with GP IIb/IIIa inhibitors were deeply investigated. The cardiovascular pathology and neuro-interventional surgical application of GP IIb/IIIa inhibitors as a class of antiplatelet agents were developed in detail. The therapeutic risk/benefit balance of currently available GP IIb/IIa receptor antagonists is not yet well elucidated in patients with ACS who are not clinically evaluated regularly for early cardiovascular revascularization. On the other hand, in patients who have benefited from PCI, the antiplatelet therapy intensification by the addition of a GP IIb/IIIa receptor antagonist (intravenously) may be an appropriate therapeutic strategy in reducing the occurrence of risks of thrombotic complications related to the intervention. Development of GP IIb/IIIa inhibitors with oral administration has the potential to include short-term antiplatelet benefits compared with intravenous GP IIb/IIIa inhibitors for long-term secondary preventive therapy in cardiovascular disease. But studies showed that long-term oral administration of GP IIb/IIIa receptor inhibitors has been ineffective in preventing ischemic events. Paradoxically, they have been linked to a high risk of side effects by producing prothrombotic and pro-inflammatory events.

Pharmacological Strategies for Stroke Intervention: Assessment of Pathophysiological Relevance and Clinical Trials

OBJECTIVES

The present review describes stroke pathophysiology in brief and discusses the spectrum of available treatments with different promising interventions that are in clinical settings or are in clinical trials.

METHODS

Relevant articles were searched using Google Scholar, Cochrane Library, and PubMed. Keywords for the search included ischemic stroke, mechanisms, stroke interventions, clinical trials, and stem cell therapy.

RESULTS AND CONCLUSION

Stroke accounts to a high burden of mortality and morbidity around the globe. Time is an important factor in treating stroke. Treatment options are limited; however, agents with considerable efficacy and tolerability are being continuously explored. With the advances in stroke interventions, new therapies are being formulated with a hope that these may aid the ongoing protective and reparative processes. Such therapies may have an extended therapeutic time window in hours, days, weeks, or longer and may have the advantage to be accessible by a majority of the patients.

The Development of Novel Drug Treatments for Stroke Patients: A Review

Acute ischemic stroke is a critical condition that can result in disability and death. The consequences of this medical condition depend on various factors, including the size of the stroke, affected brain region, treatment onset, and the type of treatment. The primary objective of stroke treatment is to restart ischemic penumbra tissue perfusion and reduce infarct volume by sustaining blood flow. Recent research on the condition's pathological pathways and processes has significantly improved treatment options beyond restoring perfusion. Many studies have concentrated on limiting injury severity via the manipulation of molecular mechanisms of ischemia, particularly in animal research. This article reviews completed and ongoing research on the development of acute ischemic stroke drugs. This study focuses on three main categories of antithrombotic drugs, thrombolytic drugs, and neuroprotective agents. The paper outlines findings from animal and clinical trials and explores the working mechanisms of these drugs.

Antiplatelet Use in Ischemic Stroke

Objective:

A literature review of antiplatelet agents for primary and secondary stroke prevention, including mechanism of action, cost, and reasons for lack of benefit.

Data sources:

Articles were gathered from MEDLINE, Cochrane Reviews, and PubMed databases (1980-2021). Abstracts from scientific meetings were considered. Search terms included ischemic stroke, aspirin, clopidogrel, dipyridamole, ticagrelor, cilostazol, prasugrel, glycoprotein IIb/IIIa inhibitors.

Study selection and data extraction:

English-language original and review articles were evaluated. Guidelines from multiple countries were reviewed. Articles were evaluated independently by 2 authors.

Data synthesis:

An abundance of evidence supports aspirin and clopidogrel use for secondary stroke prevention. In the acute phase (first 21 days postinitial stroke), these medications have higher efficacy for preventing further stroke when combined, but long-term combination therapy is associated with higher hemorrhage rates. Antiplatelet treatment failure is influenced by poor adherence and genetic polymorphisms. Antiplatelet agents such as cilostazol may provide extra benefit over clopidogrel and aspirin, in certain racial groups, but further research in more diverse ethnic populations is needed.

Relevance to patient care and clinical practice:

This review presents the data available on the use of different antiplatelet agents poststroke. Dual therapy, recurrence after initiation of secondary preventative therapy, and areas for future research are discussed.

Conclusions:

Although good evidence exists for the use of certain antiplatelet agents postischemic stroke, there are considerable opportunities for future research to investigate personalized therapies. These include screening patients for platelet polymorphisms that confer antiplatelet resistance and for randomized trials including more racially diverse populations.

Preparations from selected cucurbit vegetables as antiplatelet agents

Increased blood platelet activation plays an important role in cardiovascular diseases (CVDs). Recent experiments indicate that certain fruits and vegetables, including onion, garlic, and beetroot, have anti-platelet potential and therefore may reduce the likelihood of CVDs. While vegetables from the Cucuritaceae family are known to exerting beneficial antioxidant and anti-inflammatory effects, their effects on blood platelet activation are poorly understood. Therefore, the aim of the present study was to determine the effect on platelet adhesion of preparations from selected cucurbits: pumpkin (Cucurbita pepo; fruit without seeds), zucchini (Cucurbita pepo convar. giromontina; fruit with seeds), cucumber (Cucumis sativus; fruit with seeds), white pattypan squash (Cucurbita pepo var. patisoniana; fruit without seeds) and yellow pattypan squash (Cucurbita pepo var. patisoniana, fruit without seeds). It also evaluates the activity of these preparations on enzymatic lipid peroxidation in thrombin-activated washed blood platelets by TBARS assay. The study also determines the anti-platelet properties of these five cucurbit preparations in whole blood by flow cytometry and with the total thrombus-formation analysis system (T-TAS) and evaluates the cytotoxicity of the tested preparations against platelets based on LDH activity. The results indicate that the yellow Cucurbita pepo var. patisoniana preparation demonstrated stronger anti-platelet properties than the other tested preparations, reducing the adhesion of thrombin-activated platelets to collagen/fibrinogen, and inhibiting arachidonic acid metabolism and GPIIb/IIIa expression on 10 µM ADP-activated platelets. None of the preparations was found to cause platelet lysis. Our findings provide new information on the anti-platelet activity of the tested cucurbit preparations and their potential for treating CVDs associated with platelet hyperactivity.

Mechanisms of thrombosis and research progress on targeted antithrombotic drugs

Globally, the incidence of thromboembolic diseases has increased in recent years, accompanied by an increase in patient mortality. Currently, several targeting delivery strategies have been developed to treat thromboembolic diseases. In this review, we discuss the mechanisms of thrombolysis and current anticoagulant drugs, particularly those with targeting capability, highlighting advances in the accurate treatment of thrombolysis with fewer adverse effects. Such approaches include magnetic drug-loading systems combined with molecular imaging to recanalize blood vessels and systems based on chimeric Arg-Gly-Asp (RGD) sequences that can target platelet glycoprotein receptor. With such progress in targeted antithrombotic drugs, targeted thrombolysis treatment shows significant potential benefit for patients.

Antiplatelet agents'-ticagrelol and eptifibatide-safety in experimental colitis in mice

BACKGROUND/AIMS

To evaluate the side effects of two antiplatelet agents - ticagrelor and eptifibatide - in mice with experimentally-induced inflammatory bowel disease.

METHODS AND MATERIAL

This study was designed as a controlled, animal, drug safety investigation. C57Bl/6 mice were used to establish the ulcerative colitis model by exposure to dextran sulfate sodium (DSS), and divided into three experimental groups: eptifibatide-treated (150 µg/day intraperitoneally; n = 10), ticagrelol-treated (1 mg/day via gastric tube; n = 10), and DSS-control (plain drinking water; n = 10). An unmodeled non-DSS group served as the experimental control. Complete blood count was taken for all mice at baseline (day 0, treatment initiation) and after four days of treatment. On day 4, all animals were sacrificed for autopsy. The primary outcome measure was bleeding, and the secondary outcomes were change in platelet count, hemoglobin level, and hematocrit level.

RESULTS

Neither ticagrelor nor eptifibatide treatment produced a significant effect on DSS colitis mice for the safety parameters measured. Platelet count and hemoglobin and hematocrit levels were statistically similar between the three DSS groups and the non-DSS control group (P > 0.05). Autopsy found no evidence of recent bleeding in liver, spleen, central nervous system or serous cavities.

CONCLUSION

The antiplatelet agents ticagrelor and eptifibatide were safe in DSS colitis mice, suggesting their potential in humans suffering from ulcerative colitis, and supporting future safety studies.

Safety and Efficacy of Tirofiban in Rescue Treatment for Acute Intracranial Intraprocedural Stent Thrombosis

Background and Purpose: The incidence of acute intraprocedural stent thrombosis (AIST) during stenting of intracranial atherosclerotic stenosis (ICAS) has seldom been reported and evidence regarding the treatment of AIST is lacking. We aim to investigate the incidence of AIST during stenting of ICAS in our institute, assess the preliminary efficacy and safety of rescue treatment of tirofiban for these patients.

Methods: From September 2016 to May 2019, all symptomatic ICAS patients who underwent intracranial stenting in our institute were prospectively registered into this study, of which patients with AIST were retrospectively reviewed to extract baseline characteristics, perioperative management, procedural details, angiographic, and clinical outcomes. Rescue treatment of tirofiban for AIST was assessed by recanalization of the culprit vessel and periprocedural death, hemorrhage, and ischemic stroke.

Results: Acute intraprocedural stent thrombosis developed in 12 (6.2%) patients within 30 min after stent placement of 194 patients. All 12 cases were successfully recanalized with modified Treatment in Cerebral Ischemia (mTICI) 3 and Arterial Occlusive Lesion (AOL) 3 after rescue treatment of tirofiban alone. There was no perioperative death or any hemorrhagic complication. Three patients suffered perioperative ischemic stroke.

Conclusions: We observed a non-negligible rate of AIST during intracranial stenting procedures for ICAS. Intra-arterial bolus followed by intravenous tirofiban infusion seems to be efficacious and safe for AIST during stent placement for ICAS, without increasing the rate of hemorrhagic complications and death.

Fibrinogen for the management of critical obstetric hemorrhage

AIM

In cases of critical obstetric hemorrhage leading to extreme hypofibrinogenemia, fibrinogen is the marker that indicates the critical severity, and early fibrinogen supplementation centering on hemostatic resuscitation is a vital treatment to stabilize a catastrophic condition. In this review, we investigated the effect of fibrinogen level on hemostasis and what we can do to treat hypofibrinogenemia efficiently and improve patients' outcome.

METHODS

We reviewed numerous articles related to hypofibrinogenemia in critical obstetric hemorrhage. Especially, we performed a systematic review on target value of fibrinogen for hemostasis and effectiveness of fibrinogen concentrate. We also reviewed the articles about the methods for early normalization of fibrinogen level such as tranexamic acid, massive transfusion protocol, and point-of-care testing.

RESULTS

The target value of fibrinogen calculated by needs for massive transfusion was 200 mg/dL or 10 mm of A5_FIBTEM . Although fibrinogen concentrate worked poorly on fibrinogen levels within the normal range, it improved the blood fibrinogen levels rapidly when it was administered to critical obstetric hemorrhage patients with serious hypofibrinogenemia. Hence, the volume of FFP transfused could be reduced along with a reduction in the frequency of pulmonary edema due to volume overload.

CONCLUSION

The patient group for which fibrinogen concentrate works most effectively is cases with severe hypofibrinogenemia. Further research is required in the light of evidence. The essence of the transfusion algorithm in critical obstetric hemorrhage is to approach the target value for obtaining hemostasis, ensure an accurate and prompt grasp of the severity using point-of-care testing, introduce a massive transfusion protocol and use tranexamic acid.

Anticoagulation and Neuraxial/Peripheral Anesthesia

Novel anticoagulants (NAGs) have emerged as the preferred alternatives to vitamin K antagonists. In patients being considered for regional anesthesia, these drugs present a layer of complexity in the preprocedure evaluation. There are no established tests to monitor anticoagulant activity and our experience is short with these drugs. These authors believe it is important to review the relevant hematology, orthopedics, and anesthesiology literature to provide a valuable reference for the clinician who is met with these challenges. In addition to discussing NAGs, we also review the existing American Society of Regional Anesthesia guidelines for heparin, low-molecular-weight heparin, and antiplatelet agents.

Phase I and Phase II Therapies for Acute Ischemic Stroke: An Update on Currently Studied Drugs in Clinical Research

Acute ischemic stroke is a devastating cause of death and disability, consequences of which depend on the time from ischemia onset to treatment, the affected brain region, and its size. The main targets of ischemic stroke therapy aim to restore tissue perfusion in the ischemic penumbra in order to decrease the total infarct area by maintaining blood flow. Advances in research of pathological process and pathways during acute ischemia have resulted in improvement of new treatment strategies apart from restoring perfusion. Additionally, limiting the injury severity by manipulating the molecular mechanisms during ischemia has become a promising approach, especially in animal research. The purpose of this article is to review completed and ongoing phases I and II trials for the treatment of acute ischemic stroke, reviewing studies on antithrombotic, thrombolytic, neuroprotective, and antineuroinflammatory drugs that may translate into more effective treatments.

Rap2B GTPase: structure, functions, and regulation

Rap2B GTPase, a member of Ras-related protein superfamily, was first discovered from a platelet cDNA library in the early 1990s. Since then, it has been reported to play an important role in regulating cellular processes including cytoskeletal organization, cell growth, and proliferation. It can be stimulated and suppressed by a wide range of external and internal inducers, circulating between GTP-bound active state and GDP-bound inactive state. Increasing focus on Ras signaling pathway reveals critical effects of Rap2B on tumorigenesis. In particular, Rap2B behaves in a p53-dependent manner in regulation of apoptosis and migration. Apart from being an oncogenic activator, Rap2B has been found to participate in many other physiological events via diverse downstream effectors. In this review, we present recent studies on the structure, regulation, and multiple biological functions of Rap2B, shedding light on its potential status in treatment of cancer as well as other diseases.

Patient Evaluation and Preparation in Vascular and Interventional Radiology: What Every Interventional Radiologist Should Know (Part 2: Patient Preparation and Medications)

Performing an interventional procedure imposes a commitment on interventional radiologists to conduct the initial patient assessment, determine the best course of therapy, and provide long-term care. Patient care before and after an interventional procedure, identification, and management of early and delayed complications of various procedures are equal in importance to the procedure itself. In this second part, we complete the comprehensive, methodical review of pre-procedural care and patient preparation before vascular and interventional radiology procedures.

Cu(2+)-RGDFRGDS: exploring the mechanism and high efficacy of the nanoparticle in antithrombotic therapy

Thrombosis disease has been the leading cause of morbidity and mortality worldwide. In the discovery of antithrombotic agents, three complexes of Cu²⁺ and repetitive arginine-glycine-aspartic acid (RGD) sequences, Cu(II)-Arg-Gly-Asp-Ser-Arg-Gly-Asp-Ser (Cu[II]-4a), Cu(II)-Arg-Gly-Asp-Val-Arg-Gly-Asp-Val (Cu[II]-4b), and Cu(II)-Arg-Gly-Asp-Phe-Arg-Gly-Asp-Phe (Cu[II]-4c), were previously reported, of which Cu(II)-4a and Cu(II)-4c possessed the highest in vitro and in vivo activity, respectively. Transmission electron microscopy (TEM) images visualized that Cu(II)-4a and Cu(II)-4c formed nanoaggregates and nanoparticles, respectively. However, the details of the formation of the nanospecies complexes and of the mechanism for inhibiting thrombosis remain to be clarified. For this purpose, this study designed a novel complex of Cu(II) and the RGD octapeptide, Arg-Gly-Asp-Phe-Arg-Gly-Asp-Ser (RGDFRGDS), consisting of Arg-Gly-Asp-Phe of Cu(II)-4c and Arg-Gly-Asp-Ser of Cu(II)-4a, to colligate their biological and nanostructural benefits. In contrast with Cu(II)-4a, -4b, and -4c, Cu(II)-RGDFRGDS (Cu²⁺-FS) had high antiplatelet and antithrombotic activities, with the formed nanoparticles having a porous surface. Additionally, this paper evidenced the dimer had the basic structural unit of Cu²⁺-FS in water, theoretically simulated the formation of Cu²⁺-FS nanoparticles, and identified that Cu²⁺-FS activity in decreasing glycoprotein IIb/IIIa, P-selectin, and IL-8 was responsible for the antithrombotic action. Finally, adherence onto the surface and entry into the cytoplasm were considered the steps of a two-step model for the blocking of platelet activation by Cu²⁺-FS nanoparticles. Findings indicated that the antiplatelet aggregation activity of Cu²⁺-FS was 10–52 times higher than that of RGDFRGDS, while the effective dose for antithrombotic action was 5,000 times lower than that of RGDFRGDS.

Anti-thrombotic effects of α-linolenic acid isolated from Zanthoxylum bungeanum Maxim seeds

Background

The current study was to evaluate the anti-thrombotic effect of alpha-linolenic acid (ALA) which was isolated and purified from Jiaomu in vivo.

Methods

The seeds were crushed and subsequently subjected to saponification, acid hydrolysis, gradient freezing, urea inclusion and complexation of silver nitrate to obtain the unsaturated fatty acids. The chemical characteristics of isolated ALA were validated by ¹HNMR, ¹³CNMR and mass spectrometry, and then the anti-thrombotic effect of ALA and its mixture with linoleic acid (1:1) were evaluated in the following experiments.

Results

The alpha-linolenic acid was isolated and purified from Jiaomu through our newly established methods. ALA and its mixture with linoleic acid can prolong the hemorrhage and coagulation time as well as enhanced the survival rate of mice subjected to collagen-adrenaline induced thrombosis. In addition, the thrombosis on A-V bypass and platelet aggregation of rats will be reduced after treated with ALA or its mixture, and the expression level of Akt and PI3K protein decreased 26% and 31%, respectively.

Conclusions

We designed and optimized a very simple and high-yield procedure to isolate ALA and linoleic acid mixture from seeds of Zanthoxylum bungeanum Maxim and demonstrated that such mixture can obtain a good anti-thrombotic effect through the modulation of PI3K/Akt signaling.

Quantitative determination of clopidogrel and its metabolites in biological samples: a mini-review

Clopidogrel has been applied in antiplatelet therapy since 1998 and is the thienopyridine with the largest clinical experience. By 2011, clopidogrel (Plavix(®)) was the second top-selling drug in the world. Following complete patent expiry in 2012/2013 its use is expected to grow even further from generics entering the market. Prefaced by a brief description of clopidogrel metabolism, this review analyzes analytical methods addressing the quantification of clopidogrel and its metabolites in biological samples. Techniques that have been applied to analyze human plasma or serum are predominantly LC-MS and LC-MS/MS. The lowest level of clopidogrel quantification that has been achieved is 5pg/mL, the shortest runtime is 1.5min and almost 100% recovery has been reported using solid-phase extraction for sample preparation.

Roles of Mac-1 and glycoprotein IIb/IIIa integrins in leukocyte-platelet aggregate formation: stabilization by Mac-1 and inhibition by GpIIb/IIIa blockers

Circulating platelet-leukocyte hetero-aggregates play an important role in acute cardiovascular events and hypersensitivity reactions. The association involves the receptor families of selectins and integrin. The objective of this study was to investigate the role of CD11b/CD18 integrin (Mac-1) in hetero-aggregate formation and search for a counter-receptor on platelets ready to interact with Mac-1. As a model of leukocytes, Mac-1 presenting Chinese hamster ovary (CHO) cells were used to evaluate the role of Mac-1 in hetero-aggregate formation. The amount of CHO cell-bound active and inactive platelets was measured by flow cytometry, while the counter-receptors on platelets were identified via using blocking antibodies. We observed significant platelet adhesion on Mac-1-bearing cells when platelet-rich plasma or activated platelets were present. Inactive platelets did not adhere to Mac-1-bearing cells. Addition of fibrinogen, a ligand of Mac-1 significantly increased platelet binding. CD40L was demonstrated to act similarly on Mac-1. Inhibition of platelet GpIIb/IIIa completely abolished CHO cell-platelet aggregation. In our study, we have shown for the first time that Mac-1 mediates the formation of hetero-aggregates without selectin tethering when Mac-1 ligands such as fibrinogen or CD40L are present and blockers of platelet GpIIb/IIIa are able to diminish this interaction.

A comparison of intracoronary with intravenous glycoprotein IIb/IIIa inhibitors during percutaneous coronary intervention in patients with acute coronary syndrome: a meta-analysis of randomized controlled trials

BACKGROUND

It is still debatable whether intracoronary (IC) administration of glycoprotein IIb/IIIa inhibitors (GPIs) is superior to intravenous (IV) administration for patients with acute coronary syndrome (ACS) undergoing percutaneous coronary intervention (PCI).

METHODS

We performed a meta-analysis of randomized controlled clinical trials. A literature search was conducted for relevant trials. Primary end-points were short-term (1-3 months) and mid-/long-term (6/12 months) major adverse cardiovascular events (MACEs) (mortality, reinfarction, target vessel revascularization [TVR]). Secondary end-points were thrombolysis in myocardial infarction (TIMI) grade flow, TIMI myocardial perfusion grade (TMPG) flow, left ventricular ejection fraction (LVEF) within 2 weeks, and bleeding complication.

RESULTS

Twelve studies were included in the meta-analysis. IC administration of GPIs did not decrease short-term mortality (OR: 0.71, 95% CI: 0.41-1.23, P = 0.22) and reinfarction rate (OR: 0.76, 95% CI: 0.45-1.29, P = 0.31) compared with IV administration. There was a trend toward reduction of short-term TVR rate in IC group compared with IV group but not reaching statistical significance (OR: 0.57, 95% CI: 0.31-1.04, P = 0.07). IC administration of GPIs significantly increased TIMI grade 3 flow (OR: 1.48, 95% CI: 1.06-2.06, P = 0.02) and TMPG grade 2-3 flow (OR: 2.63, 95% CI: 1.53-4.51, P = 0.0004) compared with IV administration. No significant difference was observed in long-term MACEs rate, LVEF, and bleeding complication between the 2 groups.

CONCLUSION

IC administration of GPIs in patients with ACS undergoing PCI can significantly increase target coronary flow and myocardial reperfusion without increasing the risk of bleeding complication, but cannot improve clinical outcome compared with IV administration.

Novel agents for anti-platelet therapy

Anti-platelet therapy plays an important role in the treatment of patients with thrombotic diseases. The most commonly used anti-platelet drugs, namely, aspirin, ticlopidine, and clopidogrel, are effective in the prevention and treatment of cardio-cerebrovascular diseases. Glycoprotein IIb/IIIa antagonists (e.g., abciximab, eptifibatide and tirofiban) have demonstrated good clinical benefits and safety profiles in decreasing ischemic events in acute coronary syndrome. However, adverse events related to thrombosis or bleeding have been reported in cases of therapy with glycoprotein IIb/IIIa antagonists. Cilostazol is an anti-platelet agent used in the treatment of patients with peripheral ischemia, such as intermittent claudication. Presently, platelet adenosine diphosphate P2Y(12) receptor antagonists (e.g., clopidogrel, prasugrel, cangrelor, and ticagrelor) are being used in clinical settings for their pronounced protective effects. The new protease-activated receptor antagonists, vorapaxar and atopaxar, potentially decrease the risk of ischemic events without significantly increasing the rate of bleeding. Some other new anti-platelet drugs undergoing clinical trials have also been introduced. Indeed, the number of new anti-platelet drugs is increasing. Consequently, the efficacy of these anti-platelet agents in actual patients warrants scrutiny, especially in terms of the hemorrhagic risks. Hopefully, new selective platelet inhibitors with high anti-thrombotic efficiencies and low hemorrhagic side effects can be developed.