Search

En: Clinical & Experimental Allergy. e-ISSN 1365-2222 2021, 26 Jul : 1-15 Background: Despite the increasing incidence of anaphylaxis, its underlying molecular mechanisms and biomarkers for appropriate diagnosis remain undetermined. The rapid onset and potentially fatal outcome in the absence of managed treatment prevent its study. Up today, there are still no known biomarkers that allow an unequivocal diagnosis. Therefore, the aim of this study was to explore metabolic changes in patients suffering anaphylactic reactions depending on the trigger (food and/or drug) and severity (moderate and severe) in a real-life set-up. Methods: Eighteen episodes of anaphylaxis, one per patient, were analysed. Sera were collected during the acute phase (T1), the recovery phase (T2) and around 2–3 months after the anaphylactic reaction (T0: basal state). Reactions were classified following an exhaustive allergological evaluation for severity and trigger. Sera samples were analysed using untargeted metabolomics combining liquid chromatography coupled to mass spectrometry (LC-MS) and proton nuclear magnetic resonance spectroscopy (1 H-NMR). Results: ‘Food T1 vs T2’ and ‘moderate T1 vs T2’ anaphylaxis comparisons showed clear metabolic patterns during the onset of an anaphylactic reaction, which differed from those induced by drugs, food + drug or severe anaphylaxis. Moreover, the model of food anaphylaxis was able to distinguish the well-characterized IgE (antibiotics) from non-IgE-mediated anaphylaxis (nonsteroidal anti-inflammatory drugs), suggesting a differential metabolic pathway associated with the mechanism of action. Metabolic differences between ‘moderate vs severe’ at the acute phase T1 and at basal state T0 were studied. Among the altered metabolites, glucose, lipids, cortisol, betaine and oleamide were observed altered. Conclusions: The results of this exploratory study provide the first evidence that different anaphylactic triggers or severity induce differential metabolic changes along time or at specific time-point, respectively. Besides, the basal status T0 might identify high-risk patients, thus opening new ways to understand, diagnose and treat anaphylaxis.

Introduction Platelets are small, anucleate, cells which travel as resting discoid fragments in the blood circulation. Upon contact with an injured blood vessel, they prevent blood loss through processes of adhesion, activation and aggregation. Platelets play a central role in cardiovascular disease (CVD), both in the development of atherosclerosis and in the development of acute thrombotic events. CVD risk factors can be classed as modifiable or non-modifiable. This thesis focuses on the effect of the modifiable risk factors (physical inactivity, overweight/obesity and low cardiorespiratory fitness (CRF)) on platelet function. We investigate the role of acute exercise on platelet function, and the impact of CRF on platelet responses to acute exercise. We also explore the role of microRNA (miRNA), a subset of small non-coding RNA, in regulating platelet function in response to physical inactivity. Hypothesis Physical inactivity, overweight/obesity and low CRF adversely impact platelet function. miRNA expression could influence and modulate the platelet function response to physical inactivity. Results We performed a cross-sectional study to investigate the relationship between platelet function and lifestyle factors. High platelet counts and plateletcrit were associated with less favourable cardiovascular risk profiles, in particular with measures of overweight. Platelet adhesion was significantly increased in subjects with an overweight BMI compared to those with a healthy weight BMI. Acute strenuous aerobic exercise resulted in increased platelet adhesion and aggregation in adults and adolescents. This increase was more pronounced in those with a low CRF, particularly in adolescent subjects. Using a Dry Immersion (DI) model, we investigated the effect of acute physical inactivity on platelet function in 12 healthy males. Three days of DI resulted in significant increases in platelet count, plateletcrit, platelet adhesion, aggregation, and an elevation of platelet reactivity index (PRI) and microvesicle concentration. We identified 15 cardiovascular and inflammatory protein biomarkers whose expression levels were altered after physical inactivity. We also identified a set of 22 ‘physical inactivity’ related miRNA, which have potential targets involved in pathways associated with platelet function. Conclusion Modifiable CVD risk factors of overweight/obesity and physical inactivity elicit a prothrombotic platelet profile. CRF levels affect the platelet response to acute exercise, suggesting that habitual physical activity influences platelet function. miRNA expression can influence and modulate the platelet function response to physical inactivity by negative regulation of gene expression and could act as markers of megakaryocyte epigenetic drift.

Biomarkers encompass a wide range of different measurable indicators, representing a tangible link to physiological changes occurring within the body. Accessibility, sensitivity, and specificity are significant factors in biomarker suitability. New biomarkers continue to be discovered, and questions over appropriate selection and assessment of their usefulness remain. If traditional markers of inflammation are not sufficiently robust in their specificity, then perhaps alternative means of detection may provide more information. Epigenetic drift (epigenetic modifications as they occur as a direct function with age), and its ancillary elements, including platelets, secreted microvesicles (MVs), and microRNA (miRNA), may hold enormous predictive potential. The majority of epigenetic drift observed in blood is independent of variations in blood cell composition, addressing concerns affecting traditional blood-based biomarker efficacy. MVs are found in plasma and other biological fluids in healthy individuals. Altered MV/miRNA profiles may also be found in individuals with various diseases. Platelets are also highly reflective of physiological and lifestyle changes, making them extremely sensitive biomarkers of human health. Platelets release increased levels of MVs in response to various stimuli and under a plethora of disease states, which demonstrate a functional effect on other cell types.

Cardiovascular disease (CVD) risk factors can be classed as modifiable or non-modifiable. Physical inactivity and obesity represent major behavioural risk factors for the initiation, development and progression of CVD. Platelet dysfunction is pivotal to the aetiology of CVD, a chronic vascular inflammatory condition, which is characterised by a lag time between onset and clinical manifestation. This indicates the role of epigenetic drift, defined by stochastic patterns of gene expression not dependent on dynamic changes in coding DNA. The epigenome, a collection of chemical marks on DNA and histones, is established during embryogenesis and modified by age and lifestyle. Biogenesis and effector function of non-coding RNA, such as microRNA, play a regulatory role in gene expression and thus the epigenetic mechanism. In this chapter, we will focus on the effect of the modifiable risk factors of physical activity/inactivity and overweight/obesity on platelet function, via epigenetic changes in both megakaryocytopoiesis and thrombopoiesis. We will also discuss the role of acute exercise on platelet function and the impact of cardiorespiratory fitness (CRF) on platelet responses to acute exercise. This chapter will highlight the potential role of platelets as circulating functional biomarkers of epigenetic drift to implement, optimise and monitor CVD preventive management strategies.

Platelets are small, anucleate cells that travel as resting discoid fragments in the circulation. Their average circulating life span is 8–9 days, and their formation is an elegant and finely orchestrated series of cellular processes known as megakaryocytopoiesis and thrombopoiesis. This involves the commitment of haematopoietic stem cells, proliferation, terminal differentiation of megakaryocytic progenitors and maturation of megakaryocytes to produce functional platelets. This complex process occurs in specialised endosteal and vascular niches in the bone marrow where megakaryocytes form proplatelet projections, releasing platelets into the circulation. Upon contact with an injured blood vessel, they prevent blood loss through processes of adhesion, activation and aggregation. Platelets play a central role in cardiovascular disease (CVD), both in the development of atherosclerosis and as the cellular mediator in the development of thrombosis. Platelets have diverse roles not limited to thrombosis/haemostasis, also being involved in many vascular inflammatory conditions. Depending on the physiological context, platelet functions may be protective or contribute to adverse thrombotic and inflammatory outcomes. In this chapter, we will discuss platelets in context of their formation and function. Because of their multifaceted role in maintaining physiological homeostasis, current and development of platelet function testing platforms will be discussed.