Regulation of platelet function by catecholamines in the cerebral vasculature of the rabbit

Can we recommend mirtazapine and bupropion for patients at risk for bleeding?: A systematic review and meta-analysis

BACKGROUND

Many studies have reported that selective serotonin reuptake inhibitors (SSRI) are associated with an increased risk of bleeding. Mirtazapine and bupropion, which commonly lack serotonin reuptake inhibition, have been recommended as alternatives for patients who are at risk for bleeding. However, the evidence for these recommendations is insufficient.

METHODS

We conducted a systematic search, systematic review, and meta-analysis to investigate an evidence-based approach for the bleeding risks of mirtazapine and bupropion. From 1946 to May 2017, a total of 3981 studies were searched from PubMed, Embase, and the Cochrane Library. Among the studies, two independent reviewers selected studies per predefined eligibility criteria.

RESULTS

A total of five meta-analyses were conducted. Patients taking mirtazapine were at a greater risk of gastrointestinal bleeding (OR = 1.17, 95% CI = 1.01-1.38) than those who did not take antidepressants. No differences were observed in the bleeding risk between mirtazapine and SSRI or between bupropion and SSRI.

LIMITATIONS

The number of studies included in the meta-analysis was small.

CONCLUSION

Our results suggest that it is premature to recommend mirtazapine and bupropion for patients who have a bleeding risk. More studies with larger sample sizes and longitudinal follow-ups are warranted.

N-octanoyl-dopamine is a potent inhibitor of platelet function

Dopamine (DA) is a co-agonist for platelet activation; yet, donor DA treatment is associated with improved transplantation outcome in renal and heart recipients. Recently, N-octanoyl-dopamine (NOD) was developed which displays superior effects compared to DA in terms of graft protecting properties. Whereas DA is a known platelet co-agonist, the effect of NOD on platelet function is unknown. This is a hypothesis generating study with the aim to assess the effects and molecular mechanisms of NOD and NOD-like compounds on platelet function. The influence of DA, NOD, and NOD-like compounds on platelet responses to classical agonists (adenosine 5'-diphosphate (ADP), U46619) was investigated in six healthy donors by applying whole blood aggregometry (Multiplate®) and flow cytometry for Pac-1, CD62P, and CD63 expression. Changes in platelet cAMP concentrations were assessed by ELISA. While DA showed synergy in platelet activation by ADP and U46619, NOD caused significant inhibition of platelet function both in whole blood aggregometry and flow cytometry. The inhibitory effect of NOD was not mediated via cAMP levels. The nonredox-active NOD-analog N-octanoyl-tyramine had no effects on platelet function. Acetylated NOD conferred to NOD by intracellular esterases showed similar inhibitory effects as NOD. In contrast to DA, NOD is a potent inhibitor of platelet function most likely through intracellular redox-active processes. This adds to the overall protective effect of NOD on pre-transplantation injury and makes NOD an attractive candidate compound for donor or organ conditioning prior to transplantation.

Validating 123I-metaiodobenzylguanidine as a platelet marker for non-invasive imaging in rabbits

INTRODUCTION

Recent in vitro studies in our laboratory have demonstrated that platelets are necessary for leukocyte recruitment and airway remodelling in models of allergic airway inflammation, and also migrate to lung tissues in response to anti-IgE or relevant allergens in allergic asthma. Non-invasive imaging of platelet migration in vivo would provide a further insight into the roles of platelets in inflammatory diseases such as asthma, and metaiodobenzylguanidine (MIBG) was considered as a suitable platelet marker.

METHODS

The kinetics of MIBG uptake into rabbit platelets, the effect of MIBG on platelet function and the effect of platelet activation on MIBG uptake and retention were investigated. MIBG-labelled platelets were administered intravenously into rabbits and the time course of radioactivity in the lung and blood was monitored as a function of stimulation.

RESULTS

Following a 4h incubation of MIBG in rabbit PRP, a near maximal MIBG uptake (52.4 ± 20.2%) in platelets occurred. This time point was chosen for subsequent in vitro studies. In vitro platelet function studies showed that MIBG has no effect on ADP or PAF-induced platelet aggregation, PAF-induced thromboxane production or fMLP-induced platelet chemotaxis. However, serotonin showed a significant effect on MIBG uptake and retention, but only at high concentrations. Stimulation of rabbit platelets with ADP and PAF caused a significant release of stored MIBG in vitro. Following i.v. administration of MIBG labelled platelets, the response to i.v. ADP and PAF stimulation was small but significant.

DISCUSSION

The release of MIBG from platelets in vivo, particularly following stimulation, leads to high background levels. Therefore, MIBG may have limited utility as a label for imaging platelets in vivo using PET. However, it may be a useful marker in detecting pathological conditions where platelet migration is involved.

Platelet aggregation responses are critically regulated in vivo by endogenous nitric oxide but not by endothelial nitric oxide synthase

BACKGROUND AND PURPOSE

Although exogenous nitric oxide (NO) clearly modifies platelet function, the role and the source of endogenous NO in vivo remain undefined. In addition, endothelial NO synthase (NOS-3) critically regulates vessel tone but its role in modulating platelet function is unclear. In this paper we have investigated the roles of endogenous NO and NOS-3 in regulating platelet function in vivo and determined the functional contribution made by platelet-derived NO.

EXPERIMENTAL APPROACH

We used a mouse model for directly assessing platelet functional responses in situ in the presence of an intact vascular endothelium with supporting in vitro and molecular studies.

KEY RESULTS

Acute NOS inhibition by N(omega)-nitro-L-arginine methyl ester hydrochloride (L-NAME) enhanced platelet aggregatory responses to thrombin and platelets were shown to be regulated primarily by NO sources external to the platelet. Elevation of endogenous NOS inhibitors to mimic effects reported in patients with cardiovascular diseases did not enhance platelet responses. Platelet responsiveness following agonist stimulation was not modified in male or female NOS-3(-/-) mice but responses in NOS-3(-/-) mice were enhanced by L-NAME.

CONCLUSIONS AND IMPLICATIONS

Platelets are regulated by endogenous NO in vivo, primarily by NO originating from the environment external to the platelet with a negligible or undetectable role of platelet-derived NO. Raised levels of endogenous NOS inhibitors, as reported in a range of diseases were not, in isolation, sufficient to enhance platelet activity and NOS-3 is not essential for normal platelet function in vivo due to the presence of bioactive NO following deletion of NOS-3.

Clinically relevant concentrations of dopamine do not amplify agonist-induced human platelet Ca2+ mobilization or GP IIb IIIa activation and do not accelerate acute coronary thrombosis in dogs

BACKGROUND

Dopamine is an inotrope effective in the short term treatment of acute heart failure - including that caused by coronary artery disease. Catecholamines however can potentiate platelet activation and pre-dispose to coronary thrombosis.

AIMS

Dopamine was studied for effect on agonist induced human platelet Ca mobilization, human platelet GP iib iiia receptor activation and acute coronary thrombosis in dogs. Calcium sensitive indo-1, fluorescent immunostaining and flow cytometry were used for platelet studies while coronary thrombosis was induced in anesthetized dogs via endothelial damage, arterial wall injury and critical stenosis.

RESULTS

Dopamine 10 and 10 M had no effect on the amplitude of the platelet Ca signal evoked by thrombin 0.1 U/mL. Likewise, dopamine 10 M had no effect on GP IIb IIIa activation evoked by ADP 10 M and by thrombin 0.1 U/mL. In dogs, intravenous dopamine 8 ug/Kg/min had no effect on repetitive cycles of acute coronary thrombus formation. In positive control studies, epinephrine increased platelet responsiveness and accelerated canine coronary thrombosis.

CONCLUSION

Clinically relevant concentrations of dopamine did not amplify agonist induced human platelet Ca activation, GPiib iiia expression or experimental canine coronary thrombosis--providing a degree of reassurance concerning this versatile inotrope.

Upregulation of A2A adenosine receptors in platelets from patients affected by bipolar disorders under treatment with typical antipsychotics

Antipsychotic drugs, potent dopamine receptor antagonists, are commonly used in the treatment of psychotic and affective illness. The discovery of antagonistic interactions between A2A adenosine receptors (ARs) and D2 dopamine receptors (DRs) in the central nervous system suggests that the adenosine system may be involved in the pathogenesis of psychiatric and neurological disorders. In the present study, we demonstrated for the first time that human platelets co-express A2A ARs and D2 DRs assembled into an heteromeric complexes. We also investigated the effects of chronic treatment with either typical or atypical antipsychotics on A2A AR binding parameters and receptors responsiveness in human platelets from patients affected by bipolar disorder. Chronic administration of typical antipsychotics induced a significant upregulation of A2A AR binding sites. Since no effects on A2A AR were obtained following "in vitro" platelet treatment with a typical antipsychotic (haloperidol), we could exclude a direct effect of the drug on A2A AR at the peripheral level. Moreover, typical antipsychotics induced a significant increase in the agonist potency to mediate A2A AR-G protein coupling. On the contrary, chronic treatment with atypical antipsychotics did not induce any significant alterations in A2A AR equilibrium binding parameters and receptor responsiveness suggesting that typical but not atypical antipsychotic drugs induced a selective modification of A2A AR binding parameters in human platelets. These results are in accordance with the literature data describing the selective A2A AR upregulation induced by typical antipsychotics in human striatum suggesting platelets as a peripheral model of the interactions between adenosine and dopamine system occurring in the central nervous system.

Effekte von Dopamin auf die zelluläre und humorale Immunantwort von Patienten mit Sepsis

In vitro and in vivo studies have demonstrated that apart from its hemodynamic action dopamine can modulate immune responses. Dopamine reduces the synthesis of proinflammatory and induces the synthesis of anti-inflammatory mediators. Dopamine inhibits neurohormone synthesis, lymphocyte proliferation and platelet aggregation. It reduces the phagocytic activity of neutrophils and induces apoptosis. Particularly with regard to sepsis, where high serum dopamine levels are reached by enhanced endogenous production, exogenous application and impaired clearance, this immunomodulation may have a clinical impact. This review summarizes dopamine-mediated immunomodulating effects to advance the knowledge regarding dopamine as an immune regulator under septic conditions.

Clinical review: immunomodulatory effects of dopamine in general inflammation

Large quantitaties of inflammatory mediators are released during the course of endotoxaemia. These mediators in turn can stimulate the sympathetic nervous system (SNS) to release catecholamines, which ultimately regulate inflammation-associated impairment in tissue perfusion, myocardial impairment and vasodilatation. Treatment of sepsis is based on surgical and/or antibiotic therapy, appropriate fluid management and application of vasoactive catecholamines. With respect to the latter, discussions on the vasopressor of choice are still ongoing. Over the past decade dopamine has been considered the 'first line' vasopressor and is frequently used to improve organ perfusion and blood pressure. However, there is a growing body of evidence that dopamine has deleterious side effects; therefore, its clinical relevance seems to be more and more questionable. Nevertheless, it has not been convincingly demonstrated that other catecholamines are superior to dopamine in this respect. Apart from its haemodynamic action, dopamine can modulate immune responses by influencing the cytokine network. This leads to inhibition of expression of adhesion molecules, inhibition of cytokine and chemokine production, inhibition of neutrophil chemotaxis and disturbed T-cell proliferation. In the present review we summarize our knowledge of the immunomodulatory effects of dopamine, with an emphasis on the mechanisms by which these effects are mediated.

Type I glutaric aciduria, part 2: a model of acute striatal necrosis

Type I glutaric aciduria (GA1) is an inborn error of organic acid metabolism that is associated with acute neurological crises, typically precipitated by an infectious illness. The neurological crisis coincides with swelling, metabolic depression, and necrosis of basal ganglia gray matter, especially the putamina and can be visualized as focal, stroke-like, signal hyperintensity on MRI. Here we focus on the stroke-like nature of striatal necrosis and its similarity to brain injury that occurs in infants after hypoxia-ischemia or systemic intoxication with 3-nitropropionic acid (NPA). These conditions share several features including abrupt onset, preferential effect in the striatum and age-specific susceptibility. The pathophysiology of the conditions is reviewed and a model proposed herein. We encourage investigators to test this model in an appropriate experimental system.