Editorial: Platelet Secretion

Exposure to Electronic Waterpipes Increases the Risk of Occlusive Cardiovascular Disease in C57BL/6J Mice

INTRODUCTION

It is well documented that cardiovascular disease (CVD) is the leading cause of death in the US and worldwide, with smoking being the most preventable cause. Additionally, most smokers die from thrombotic-based diseases, in which platelets play a major role. To this end, because of the proven harm of smoking, several novel tobacco products such as electronic(e)-waterpipe have been gaining popularity among different sectors of the population, partly due to their "false" safety claims. While many investigators have focused on the negative health effects of traditional cigarettes and e-cigarettes on the cardiovascular system, virtually little or nothing is known about e-waterpipes, which we investigated herein.

METHODS AND MATERIALS

To investigate their occlusive CVD effects, we employed a whole-body mouse exposure model of e-waterpipe vape/smoke and exposed C57BL/6J male mice (starting at 7 weeks of age) for 1 month, with the controls exposed to clean air. Exposures took place seven times a week, according to the well-known Beirut protocol, which has been employed in many studies, as it mimics real-life waterpipe exposure scenarios; specifically, 171 puffs of 530 ml volume of the e-liquid at 2.6 s puff duration and 17 s puff interval.

RESULTS

The e-waterpipe exposed mice had shortened bleeding and occlusion times, when compared to the clean air controls, indicating a prothrombotic phenotype. As for the mechanism underlying this phenotype, we found that e-waterpipe exposed platelets exhibited enhanced agonist-triggered aggregation and dense granule secretion. Also, flow cytometry analysis of surface markers of platelet activation showed that both P-selectin and integrin GPIIb-IIIa activation were enhanced in the e-waterpipe exposed platelets, relative to the controls. Finally, platelet spreading and Akt phosphorylation were also more pronounced in the exposed mice.

CONCLUSION

We document that e-waterpipe exposure does exert untoward effects in the context of thrombosis-based CVD, in part, via promoting platelet hyperreactivity.

A Novel Antibody Targeting the Second Extracellular Loop of the Serotonin 5-HT2A Receptor Inhibits Platelet Function

Serotonin (5-hydroxytriptamine or 5-HT) is known to be a weak platelet agonist, and is involved in thrombus formation. While 5-HT cannot induce platelet aggregation on its own, when secreted from the alpha granules, it binds to its G-protein Coupled Receptor (GPCR; i.e., 5HT_2AR), thereby acting to amplify platelet functional responses (e.g., aggregation). Thus, 5HT_2AR-mediated responses are more involved in the secondary amplification of platelet aggregation in the growing thrombus. Therefore, even though 5-HT can be seen as a weak inducer of platelet activation, it is an important amplifier of aggregation triggered by agonists such as ADP, collagen, and epinephrine, thereby enhancing thrombogenesis. The 5HT_2AR/5HT_2A signaling pathway is of clinical interest to the scientific and medical communities as it has been implicated in the genesis of several forms of cardiovascular disorders. However, efforts to develop antagonists for 5HT_2AR as therapeutic agents in cardiovascular diseases have thus far failed due to these reagents having deleterious side-effects, and/or to lack of selectivity, amongst other reasons. In light of research efforts that identified that the 5HT_2AR ligand binding domain resides in the second extracellular loop (EL2; amino acids P²⁰⁹-N²³³), we developed an antibody, i.e., referred to as 5HT_2ARAb, against the EL2 region, and characterized its pharmacological activity in the context of platelets. Thus, we utilized platelets from healthy human donors, as well as C57BL/6J mice (10-12 weeks old) to analyze the inhibitory effects of the 5HT_2ARAb on platelet activation in vitro, ex vivo, and on thrombogenesis in vivo as well as on 5HT_2AR ligand binding. Our results indicate that the 5HT_2ARAb inhibits 5-HT-enhanced platelet activation in vitro and ex vivo, but has no apparent effects on that which is agonist-induced. The 5HT_2ARAb was also found to prolong the thrombus occlusion time, and it did so without modulating the tail bleeding time, in mice unlike the P2Y12 antagonist clopidogrel and the 5HT_2AR antagonist ketanserin. Moreover, it was found that the 5HT_2ARAb does so by directly antagonizing the platelet 5HT_2AR. Our findings document that the custom-made 5HT_2ARAb exhibits platelet function blocking activity and protects against thrombogenesis without impairing normal hemostasis.

The Antidepressant Duloxetine Inhibits Platelet Function and Protects against Thrombosis

While cardiovascular disease (CVD) is the leading cause of death, major depressive disorder (MDD) is the primary cause of disability, affecting more than 300 million people worldwide. Interestingly, there is evidence that CVD is more prevalent in people with MDD. It is well established that neurotransmitters, namely serotonin and norepinephrine, are involved in the biochemical mechanisms of MDD, and consequently, drugs targeting serotonin-norepinephrine reuptake, such as duloxetine, are commonly prescribed for MDD. In this connection, serotonin and norepinephrine are also known to play critical roles in primary hemostasis. Based on these considerations, we investigated if duloxetine can be repurposed as an antiplatelet medication. Our results-using human and/or mouse platelets show that duloxetine dose-dependently inhibited agonist-induced platelet aggregation, compared to the vehicle control. Furthermore, it also blocked agonist-induced dense and α-granule secretion, integrin αIIbβ3 activation, phosphatidylserine expression, and clot retraction. Moreover duloxetine-treated mice had a significantly prolonged occlusion time. Finally, duloxetine was also found to impair hemostasis. Collectively, our data indicate that the antidepressant duloxetine, which is a serotonin-norepinephrine antagonist, exerts antiplatelet and thromboprotective effects and inhibits hemostasis. Consequently, duloxetine, or a rationally designed derivative, presents potential benefits in the context of CVD, including that associated with MDD.

Short-Term Exposure to Waterpipe/Hookah Smoke Triggers a Hyperactive Platelet Activation State and Increases the Risk of Thrombogenesis

OBJECTIVE

Cardiovascular disease is a major public health problem. Among cardiovascular disease's risk factors, tobacco smoking is considered the single most preventable cause of death, with thrombosis being the main mechanism of cardiovascular disease mortality in smokers. While tobacco smoking has been on the decline, the use of waterpipes/hookah has been rising, mainly due to the perception that they are less harmful than regular cigarettes. Strikingly, there are few studies on the negative effects of waterpipes on the cardiovascular system, and none regarding their direct contribution to thrombus formation. Approach and Results: We used a waterpipe whole-body exposure protocol that mimics real-life human exposure scenarios and investigated its effects, relative to clean air, on platelet function, hemostasis, and thrombogenesis. We found that waterpipe smoke (WPS)-exposed mice exhibited both shortened thrombus occlusion and bleeding times. Further, our results show that platelets from WPS-exposed mice are hyperactive, with enhanced agonist-induced aggregation, dense and α-granule secretion, αIIbβ3 integrin activation, phosphatidylserine expression, and platelet spreading, when compared with clean air-exposed platelets. Finally, at the molecular level, it was found that Akt (protein kinase B) and ERK (extracellular signal-regulated kinases) phosphorylation are enhanced in the WPS and in nicotine-treated platelets.

CONCLUSIONS

Our findings demonstrate that WPS exposure directly modulates hemostasis and increases the risk of thrombosis and that this is mediated, in part, via a state of platelet hyperactivity. The negative health impact of WPS/hookah, therefore, should not be underestimated. Moreover, this study should also help in raising public awareness of the toxic effects of waterpipe/hookah.

Arhgef1 Plays a Vital Role in Platelet Function and Thrombogenesis

Background Platelets are the cellular mediators of hemostasis and thrombosis, and their function is regulated by a number of molecular mediators, such as small GTP ases. These small GTP ases are themselves regulated by guanine nucleotide exchange factors such as Arhgefs, several of which are found in platelets, including the highly expressed Arhgef1. However, the role of Arhgef1 in platelets has not yet been investigated. Methods and Results We employed mice with genetic deletion of Arhgef1 (ie, Arhgef1-/-) and investigated their platelet phenotype by employing a host of in vivo and in vitro platelet assays. Our results indicate that Arhgef1-/- mice had prolonged carotid artery occlusion and tail bleeding times. Moreover, platelets from these mice exhibited defective aggregation, dense and α granule secretion, α II bβ3 integrin activation, clot retraction and spreading, in comparison to their wild-type littermates. Finally, we also found that the mechanism by which Arhgef1 regulates platelets is mediated in part by a defect in the activation of the RhoA-Rho-associated kinase axis, but not Rap1b. Conclusions Our data demonstrate, for the first time, that Arhgef1 plays a critical role in platelet function, in vitro and in vivo.

Short-Term E-Cigarette Exposure Increases the Risk of Thrombogenesis and Enhances Platelet Function in Mice

Background

Cardiovascular disease is the main cause of death in the United States, with smoking being the primary preventable cause of premature death, and thrombosis being the main mechanism of cardiovascular mortality in smokers. Due to the perception that electronic/e‐cigarettes are “safer/less harmful” than conventional cigarettes, their usage—among a variety of ages—has increased tremendously during the past decade. Notably, there are limited studies regarding the negative effects of e‐cigarettes on the cardiovascular system, which is also the subject of significant debate.

Methods and Results

We employed a passive e‐Vape^TM vapor inhalation system and developed an in vivo whole‐body e‐cigarette mouse exposure protocol that mimics real‐life human exposure scenarios/conditions and investigated the effects of e‐cigarettes and clean air on platelet function and thrombogenesis. Our results show that platelets from e‐cigarette–exposed mice are hyperactive, with enhanced aggregation, dense and α granule secretion, activation of the αIIbβ3 integrin, phosphatidylserine expression, and Akt and ERK activation, when compared with clean air–exposed platelets. E‐cigarette–exposed platelets were also found to be resistant to inhibition by prostacyclin, relative to clean air. Furthermore, the e‐cigarette–exposed mice exhibited a shortened thrombosis occlusion and bleeding times.

Conclusions

Taken together, our data demonstrate for the first time that e‐cigarettes alter physiological hemostasis and increase the risk of thrombogenic events. This is attributable, at least in part, to the hyperactive state of platelets. Thus, the negative health consequences of e‐cigarette exposure should not be underestimated and warrant further investigation.

Platelet Releasate Proteome Profiling Reveals a Core Set of Proteins with Low Variance between Healthy Adults

Upon activation, platelets release a powerful cocktail of soluble and vesicular signals, collectively termed the "platelet releasate" (PR). Although several studies have used qualitative/quantitative proteomic approaches to characterize PR; with debated content and significant inter-individual variability reported, confident, and reliable insights have been hindered. Using label-free quantitative (LFQ)-proteomics analysis, a reproducible, quantifiable investigation of the 1U mL^-1 thrombin-induced PR from 32 healthy adults was conducted. MS proteomics data are available via ProteomeXchange, identifier PXD009310. Of the 894 proteins identified, 277 proteins were quantified across all donors and form a "core" PR. Bioinformatics and further LFQ-proteomic analysis revealed that the majority (84%) of "core" PR proteins overlapped with the protein composition of human platelet-derived exosomes. Vesicles in the exosomal-size range were confirmed in healthy-human PR and reduced numbers of similar-sized vesicles were observed in the PR of a mouse model of gray platelet syndrome, known to be deficient in platelet alpha-granules. Lastly, the variability of proteins in the PR was assessed, and reproducible secretion levels were found across all 32 healthy donors. Taken together, the PR contains valuable soluble and vesicular cargo and has low-population variance among healthy adults, rendering it a potentially useful platform for diagnostic fingerprinting of platelet-related disease.