In the past few decades, the incidence, morbidity, and mortality of acute brain stroke have been rising year by year. 25% of AIS is caused by large artery atherosclerotic stenosis, which is closely related to platelet aggregation[22, 23]. So antiplatelet treatment is indispensable in the management of patients with AIS.
Currently, aspirin is one of the most commonly used antiplatelet drugs, whose mechanism is to inhabit cyclooxygenase-1 (COX-1) and − 2 (COX-2) isozyme activity irreversibly. This promotes the process of the conversion of AA into prostaglandin 2, in turn, blocks the production of TxA2[24, 25]. So, the AA-induced aggregation test is regarded as a method to evaluate the antiplatelet function of aspirin.
Neuro-protection, as a novel treatment strategy, has been an essential portion of the management of AIS nowadays. Various phytochemicals have been found to not only exert neuro-protective effects but also show positive effects against atherosclerosis, which may be associated with the inhibition of AA-induced platelet aggregation. For example, flavonoids are involved in the AA cascade, related to the activity of both COX and TxA2[26]. Green tea was found to be related to antiplatelet activity in vitro and ex vivo because of the presence of flavonoids[27].
GBE, whose mean active components are flavonoids, was one of the popular natural products in America[28]. GBE could be involved in reducing brain edema, anti-inflammation and so on [10–12]. GBE is now typically regarded as auxiliary medicine often combined with aspirin in clinical setting in the management of AIS.
Ke J found that GBE acts similarly to aspirin, demonstrating an antiplatelet effect in mice when stimulated by AA agonists [18], while Kim Y.S found that GBE showed no synergistic effect against platelet aggregation when stimulated by ADP agonists when combined with ticlopidine[19]. However, there is rare research on its antiplatelet activity and possible mechanisms on humans up to now.
The management mentioned above has saved multiple lives around the world, however, it brings a lot of bleeding events that should be paid attention to. To avoid this adverse effect, the soft-gel capsules of aspirin were produced as an effective and safe alternative[29].
The application of GBE and/or aspirin could cause bleeding events including hemorrhagic stroke, gastrointestinal bleeding, and so on [6, 7].
For those reasons, herein we evaluated the effects of GBE on AA-induced and ADP-induced platelet aggregation in patients. Meanwhile, to rule out other possible targets of GBE-related bleeding events, we evaluated the effects of GBE on other platelet indices (BPC, PDW, MPV, and PLC) and coagulation markers (PT, TT, PTA, and APTT). And then, we evaluated the effects of GBE combined with aspirin, as well as, bleeding events related to the combination of aspirin and GBE. The findings from our study make GBE better understood, which could finally contribute to make more proper strategies of GBE and antiplatelet agent use and reduce the risk of treatment-related bleeding events.
We monitored the effects of GBE on platelet indices by comparing the data between baseline, and the first day and the fifth day post-treatment. Our results showed that GBE produced notable antiplatelet effects on AA-induced platelet aggregation but no significant effects on other platelet indices (Table 2). And had mildly anticoagulation effect, TT showed a increasing at day1, and APTT was higher than baseline at both day 1 and 5 when compared to the baseline (Fig. 3).
Synergy group compared to aspirin group, we found that GBE combined with aspirin can more strongly inhibit AA-induced platelet aggregation than that in aspirin group. Moreover, bleeding events increased in the former group (4 events) than that in the later group (0 event) (Table 4).
Guerrero, J. A et.al found that the mechanism of the antiplatelet function of flavonoids may originate from the flavonoid-TP interaction, which depends on the presence of hydroxyl radicals on carbons 7 and 4′ in the active structure of the flavonoid skeleton. [16]
These results could explain the effect of GBE on AA-induced platelet aggregation and the reason why in the circumstance of the application of aspirin, GBE can further reduce the platelet aggregation induced by AA. In this scenario, TP receptors are inhibited, but the platelet survival time is 7–10 days[30], which could explain why AA-induced platelet aggregation could sustain a relatively low level after the application of GBE.
However, contrary to the results of this study, Kellermann et al and Kohler et al found that GBE did not affect coagulation function compared with placebo[31, 32].
When it comes to the bleeding events caused by GBE combined with aspirin, we hold the view that it may be related to the further decreased platelet aggregation, however, more studies are still ongoing to confirm this hypothesis.
To sum up, the main findings in this study included (1) GBE inhibited AA-induced platelet aggregation in some degree, and had no influence on ADP-induced platelet aggregation. (2) GBE could synergize with aspirin in the suppression in AA pass way. (3) The combination of GBE and aspirin may increase the incidence of bleeding. (4) The mechanisms underlying the effects of GBE on TT and APTT require further investigation.
Dynamic monitoring of plasma AA-induced platelet aggregation in the patients who underwent the combination of GBE and aspirin may helpful on inhibiting treatment- related bleeding events, so as to adjust the dosages of both GBE and aspirin according to the dynamic data of AA-induced platelet aggregation, further study with large case number of the patients is still ongoing to identity the conclusion.
Limitation:
Several limitations in the present study need to be addressed. Firstly, though light transmission aggregometry (LTA) is the gold standard for platelet aggregation, there still exist unavoidable errors, so more precise tests are needed. Additionally, as this study was mainly carried out among patients with a Han Chinese background, data from other ethnic groups is needed for further study. Finally, the case number is small, so further study with large case number is still ongoing.
Authors’ contributions:
XH wrote the first draft of the manuscript; XH, XZ, LD, and MW performed the material preparation, data collection, and statistical analysis; DZ, RM, and XJ contributed to imaging assessments; RM and YD wrote sections of the manuscript and contributed to manuscript revision; RM contributed to manuscript drafting and revision, and study concept and design.