Differential physiological changes following internet exposure in higher and lower problematic internet users

Problematic internet use (PIU) has been suggested as in need of further research with a view to being included as a disorder in future Diagnostic and Statistical Manual (DSM) of the American Psychiatric Association, but lack of knowledge about the impact of internet cessation on physiological function remains a major gap in knowledge and a barrier to PIU classification. One hundred and forty-four participants were assessed for physiological (blood pressure and heart rate) and psychological (mood and state anxiety) function before and after an internet session. Individuals also completed a psychometric examination relating to their usage of the internet, as well as their levels of depression and trait anxiety. Individuals who identified themselves as having PIU displayed increases in heart rate and systolic blood pressure, as well as reduced mood and increased state of anxiety, following cessation of internet session. There were no such changes in individuals with no self-reported PIU. These changes were independent of levels of depression and trait anxiety. These changes after cessation of internet use are similar to those seen in individuals who have ceased using sedative or opiate drugs, and suggest PIU deserves further investigation and serious consideration as a disorder

Perivascular niche cells sense thrombocytopenia and activate hematopoietic stem cells in an IL-1 dependent manner

Hematopoietic stem cells (HSCs) residing in specialized niches in the bone marrow are responsible for the balanced output of multiple short-lived blood cell lineages in steady-state and in response to different challenges. However, feedback mechanisms by which HSCs, through their niches, sense acute losses of specific blood cell lineages remain to be established. While all HSCs replenish platelets, previous studies have shown that a large fraction of HSCs are molecularly primed for the megakaryocyte-platelet lineage and are rapidly recruited into proliferation upon platelet depletion. Platelets normally turnover in an activation-dependent manner, herein mimicked by antibodies inducing platelet activation and depletion. Antibody-mediated platelet activation upregulates expression of Interleukin-1 (IL-1) in platelets, and in bone marrow extracellular fluid in vivo. Genetic experiments demonstrate that rather than IL-1 directly activating HSCs, activation of bone marrow Lepr+ perivascular niche cells expressing IL-1 receptor is critical for the optimal activation of quiescent HSCs upon platelet activation and depletion. These findings identify a feedback mechanism by which activation-induced depletion of a mature blood cell lineage leads to a niche-dependent activation of HSCs to reinstate its homeostasis

Plant Food Delphinidin-3-Glucoside Significantly Inhibits Platelet Activation and Thrombosis: Novel Protective Roles against Cardiovascular Diseases

Delphinidin-3-glucoside (Dp-3-g) is one of the predominant bioactive compounds of anthocyanins in many plant foods. Although several anthocyanin compounds have been reported to be protective against cardiovascular diseases (CVDs), the direct effect of anthocyanins on platelets, the key players in atherothrombosis, has not been studied. The roles of Dp-3-g in platelet function are completely unknown. The present study investigated the effects of Dp-3-g on platelet activation and several thrombosis models in vitro and in vivo. We found that Dp-3-g significantly inhibited human and murine platelet aggregation in both platelet-rich plasma and purified platelets. It also markedly reduced thrombus growth in human and murine blood in perfusion chambers at both low and high shear rates. Using intravital microscopy, we observed that Dp-3-g decreased platelet deposition, destabilized thrombi, and prolonged the time required for vessel occlusion. Dp-3-g also significantly inhibited thrombus growth in a carotid artery thrombosis model. To elucidate the mechanisms, we examined platelet activation markers via flow cytometry and found that Dp-3-g significantly inhibited the expression of P-selectin, CD63, CD40L, which reflect platelet α- and δ-granule release, and cytosol protein secretion, respectively. We further demonstrated that Dp-3-g downregulated the expression of active integrin αIIbβ3 on platelets, and attenuated fibrinogen binding to platelets following agonist treatment, without interfering with the direct interaction between fibrinogen and integrin αIIbβ3. We found that Dp-3-g reduced phosphorylation of adenosine monophosphate-activated protein kinase, which may contribute to the observed inhibitory effects on platelet activation. Thus, Dp-3-g significantly inhibits platelet activation and attenuates thrombus growth at both arterial and venous shear stresses, which likely contributes to its protective roles against thrombosis and CVDs

Snake Venom Botrocetin Induces GPIb-Independent Platelet Aggregation

Abstract Abstract Introduction：Snake venom-derived botrocetin facilitates von Willebrand factor (VWF) binding to GPIbα, and has been used clinically for the detection of von Willebrand disease (VWD) and GPIb-related disorders. Botrocetin has also been widely used experimentally for the development and characterization of potential antithrombotic drugs targeting the GPIb-VWF axis. Although compelling evidence suggests GPIb is responsible for botrocetin-induced VWF binding and platelet aggregation, some reports suggest that botrocetin could induce platelet aggregation in some Bernard-Soulier syndrome (BSS) patients who lack a functional GPIb complex. However, the alternative mechanism for botrocetin-induced BSS platelet aggregation and the receptor(s) mediating this action are unclear. Methods: Botrocetin was purified from the lyophilized venom of Bothrops jararaca using ion-exchange column chromatography. Light transmission aggregometry assay was performed using platelet-rich plasma (PRP) from human, wild type (WT) mice, GPIbα-deficient mice, αIIbβ3-deficient mice and VWF-deficient mice, or CHO cells stably transfected with αIIbβ3 integrin. O-sialoglycoprotein endopeptidase (OSGE) was used to cleave the N-terminal extracellular domain of GPIbα. The binding of botrocetin, VWF and fibrinogen to platelets from WT or the gene-deficient mice were measured by flow cytometry. Antibodies against GPIbα (SZ2, NIT A) and integrin αIIbβ3 (abciximab, JON/A, M1, PSI E1) were used to investigate the binding site of botrocetin. Perfusion chamber assay was used to measure thrombus formation under different shear stresses. Results: We discovered that botrocetin induced aggregation of human platelets lacking the N-terminal extracellular domain of GPIbα and platelets from GPIbα-deficient mice in the presence of VWF. This VWF-dependent, GPIbα-independent platelet aggregation induced by botrocetin was inhibited by αIIbβ3 antagonists. Botrocetin also induced aggregation of CHO cells stably transfected with αIIbβ3 in VWF-dependent manner. Further experiments with gel-filtered platelets showed that botrocetin competitively bound to the ligand-binding area exposed on αIIbβ3 and blocked fibrinogen and other ligands from binding to the active state of αIIbβ3 in the absence of VWF. Botrocetin inhibited platelet aggregation and thrombus formation in VWF-deficient mice. Conclusion: Integrin αIIbβ3 is the alternative receptor that mediates VWF-dependent, GPIb-independent platelet aggregation induced by botrocetin. However, via targeting αIIbβ3, botrocetin itself inhibits platelet aggregation in the absence of VWF. These results demonstrate versatility in the mechanism of botrocetin, which may provide snakes containing this toxin the adaptability necessary to aggregate platelets/thrombocytes of different prey or predators. Our data reveals a previously unknown role of botrocetin in the integrin-VWF interaction and also provides insight into developing new antithrombotic drugs that target the active conformation of integrin αIIbβ3. The target switching of botrocetin between GPIb-VWF and αIIbβ3-VWF may explain the possible misdiagnosis of the GPIb-related congenital disorders evaluated by botrocetin. Disclosures No relevant conflicts of interest to declare. </jats:sec

Targeting β3 Integrin Psi Domain Inhibits Both Platelet Aggregation and Blood Coagulation: Two Birds with One Stone

Abstract Integrin αIIbβ3 plays key roles in thrombosis and hemostasis primarily through mediating platelet adhesion and aggregation. We recently reported that the active site of thiol-isomerase enzymes, CXXC motif, is expressed twice within the plexin-semaphorin-integrin (PSI) domain across all integrins and species, and the PSI domain of β3 integrin possesses endogenous thiol-isomerase activity, which may be a novel target for anti-thrombotic therapy (Blood, 2017). We developed four mouse anti-mouse β3 integrin PSI domain monoclonal antibodies (mAbs). These mAbs cross-react with β3 PSI domains of human, mouse, pig, rat, and rabbit tested but not other regions of β3 integrin, other integrins or other thiol-isomerase enzymes. They inhibit the thiol-isomerase activity of β3 PSI domain, decrease platelet adhesion/aggregation and thrombosis without increasing bleeding. Interestingly, the inhibitory effect of these mAbs on thrombosis in vivo (no anti-coagulant) was 10-20 times greater than their inhibitory effect on platelet aggregation in anti-coagulated platelet-rich plasma in vitro. This motivated us to explore whether this PSI domain contributes to blood coagulation. To asses blood clot formation and retraction, blood was incubated in non-stick tubes for two hours at 37°C in clot retraction assays. These assays showed less clot retraction and significantly lower dry clot weight in human and mouse whole blood treated with these anti-PSI mAbs compared to controls (p&lt;0.05). As a visual representation, laser scanning confocal microscopy of platelet-rich plasma samples with labelled fibrinogen/fibrin showed that fibrin network formation of anti-PSI mAb treated clots was decreased. To measure blood coagulation in a global assay in the presence of platelets and natural blood constituents, thromboelastography (TEG) was performed. Blinded TEG showed that anti-PSI mAb-treated whole blood (human and mouse) and platelet rich plasma (human) decreased in coagulation compared to controls (p&lt;0.05). We further compared our anti-PSI mAbs with other anti-β3 integrin mAbs that inhibit αIIbβ3 ligand binding and platelet aggregation much stronger than the anti-PSI mAbs. In this TEG assay we found that the anti-PSI mAbs were still significantly decreasing platelet coagulation parameters, much more than other inhibitory anti-β3 mAbs including M1 and JAN D1 as well as the Abciximab precursor 7E3 (p&lt;0.05). This suggests the decreased coagulation may result from the anti-thiol-isomerase activity of the anti-PSI mAbs. Disulfide bond exchanges are required for blood coagulation and thiol-isomerase enzymes play important roles in thrombosis. Given that blood coagulation is rapidly amplified on the platelet surface (i.e. cell-based coagulation), many coagulation factors are in close proximity to β3 integrin PSI domains (with thiol-isomerase activity). The study of interaction between β3 PSI domain and coagulation factors is currently being exploring. This is the first evidence of an allosteric therapeutic target of β3 integrin. This work suggests that a novel interaction exists between platelets and the coagulation cascade that requires the β3 integrin PSI domain and its thiol-isomerase activity. Importantly, the PSI domain can be targeted to partially block both platelet aggregation and coagulation, resulting in less bleeding while still providing a strong overall anti-thrombotic effect. Disclosures No relevant conflicts of interest to declare. </jats:sec