Combination aspirin and clopidogrel for secondary prevention of ischemic stroke

Monitoring Antiplatelet Aggregation In Vivo and In Vitro by Microtiter Plate Method

BACKGROUND

The current light transmission aggregation method is a recognized conventional method for platelet function evaluation, but it is time-consuming and poor in parallelism and cannot simultaneously monitor multiple inducers at multiple levels. The microtiter plate method has been established because of the high-throughput characteristic, but it needs more practical applications.

OBJECTIVES

To evaluate the microtiter plate method by using aspirin and clopidogrel in vivo and in vitro.

METHODS

In vitro, the platelet aggregations inhibited by aspirin (0.3, 1, 3, 10, 30, 90 μM) and clopidogrel (1, 3, 10, 30, 100, 300 μM) were evaluated with the presence of arachidonic acid (AA) and adenosine diphosphate (ADP) agonists. Using the combination index (CI), the effect of the combination of aspirin and clopidogrel on platelet aggregation was evaluated. In vivo, New Zealand rabbits (n = 18) were randomly divided into 3 groups, aspirin group (5 mg/kg, intragastrical gavage [i.g.]), clopidogrel group (14 mg/kg at the first day, followed by 4 mg/kg, i.g.), and the combination of these two drugs, administered (i.g.) continuously for 7 days. Then, the blood was collected to measure platelet aggregation.

RESULTS

Different concentrations of AA (12.5, 25, 50, 100 μM) and ADP (1.25, 2.5, 5, 10 μM) could promote platelet aggregation in concentration-dependent manner, and the most stable induction concentrations of AA and ADP were 50 and 5 μM. In vitro, with the above optimized detection system, aspirin and clopidogrel alone or in combination had concentration-dependent antiplatelet aggregation. The combination of aspirin and clopidogrel also showed synergistic inhibition effect within the concentration range studied. In vivo, aspirin and clopidogrel alone or in combination inhibited platelet aggregation induced by multiple concentrations of AA and ADP agonists, and the combined inhibition was more significant during the administration than aspirin or clopidogrel alone.

CONCLUSIONS

The improved microtiter plate method combining the use of multiple levels of multiple agonists avoids the variation of the effective inducer concentrations due to individual different response of platelets to agonists. It may be a potential approach in the detection of platelet aggregation.

Treatment Approaches to Lacunar Stroke

Lacunar strokes are appropriately named for their ability to cavitate and form ponds or "little lakes" (Latin: lacune -ae meaning pond or pit is a diminutive form of lacus meaning lake). They account for a substantial proportion of both symptomatic and asymptomatic ischemic strokes. In recent years, there have been several advances in the management of large vessel occlusions. New therapies such as non-vitamin K antagonist oral anticoagulants and left atrial appendage closure have recently been developed to improve stroke prevention in atrial fibrillation; however, the treatment of small vessel disease-related strokes lags frustratingly behind. Since Fisher characterized the lacunar syndromes and associated infarcts in the late 1960s, there have been no therapies specifically targeting lacunar stroke. Unfortunately, many therapeutic agents used for the treatment of ischemic stroke in general offer only a modest benefit in reducing recurrent stroke while adding to the risk of intracerebral hemorrhage and systemic bleeding. Escalation of antithrombotic treatments beyond standard single antiplatelet agents has not been effective in long-term lacunar stroke prevention efforts, unequivocally increasing intracerebral hemorrhage risk without providing a significant benefit. In this review, we critically review the available treatments for lacunar stroke based on evidence from clinical trials. For several of the major drugs, we summarize the adverse effects in the context of this unique patient population. We also discuss the role of neuroprotective therapies and neural repair strategies as they may relate to recovery from lacunar stroke.

New approaches in tail-bleeding assay in mice: improving an important method for designing new anti-thrombotic agents

This report describes a modified, simple, low-cost and more sensitive method to determine bleeding patterns and haemoglobin concentration in a tail-bleeding assay using BALB/c mice and tail tip amputation. The cut tail was immersed in Drabkin's reagent to promote erythrocyte lysis and haemoglobin release, which was monitored over 30 min. The operator was blinded to individual conditions of the mice, which were treated with either saline (NaCl 0.15m), DMSO (0.5%) or clinical anti-thrombotic drugs. Our experimental protocols showed good reproducibility and repeatability of results when using Drabkin's reagent than water. Thus, the use of Drabkin's reagent offered a simple and low-cost method to observe and quantify the bleeding and rebleeding episodes. We also observed the bleeding pattern and total haemoglobin loss using untreated animals or those under anti-coagulant therapy in order to validate the new Drabkin method and thus confirm that it is a useful protocol to quantify haemoglobin concentrations in tail-bleeding assay. This modified method provided a more accurate results for bleeding patterns in mice and for identifying new anti-thrombotic drugs.

Interleukin-6 mediates enhanced thrombus development in cerebral arterioles following a brief period of focal brain ischemia

OBJECTIVE

The cerebral microvasculature is rendered more vulnerable to thrombus formation following a brief (5.0 min) period of focal ischemia. This study examined the contribution of interleukin-6 (IL-6), a neuroprotective and prothrombotic cytokine produced by the brain, to transient ischemia-induced thrombosis in cerebral arterioles.

APPROACH & RESULTS

The middle cerebral artery of C57BL/6J mice was occluded for 5 min, followed by 24h of reperfusion (MCAo/R). Intravital fluorescence microscopy was used to monitor thrombus development in cerebral arterioles induced by light/dye photoactivation. Thrombosis was quantified as the time of onset of platelet aggregation on the vessel wall and the time for complete blood flow cessation. MCAo/R in wild type (WT) mice yielded an acceleration of thrombus formation that was accompanied by increased IL-6 levels in plasma and in post-ischemic brain tissue. The exaggerated thrombosis response to MCAo/R was blunted in WT mice receiving an IL-6 receptor-blocking antibody and in IL-6 deficient (IL-6(-/-)) mice. Bone marrow chimeras, produced by transplanting IL-6(-/-) marrow into WT recipients, did not exhibit protection against MCAo/R-induced thrombosis.

CONCLUSIONS

The increased vulnerability of the cerebral vasculature to thrombus development after MCAo/R is mediated by IL-6, which is likely derived from brain cells rather than circulating blood cells. These findings suggest that anti-IL-6 therapy may reduce the likelihood of cerebral thrombus development after a transient ischemic attack.