Splenic release of platelets contributes to increased circulating platelet size and inflammation after myocardial infarction

The role and mechanisms of microvascular damage in the ischemic myocardium

Following myocardial ischemic injury, the most effective clinical intervention is timely restoration of blood perfusion to ischemic but viable myocardium to reduce irreversible myocardial necrosis, limit infarct size, and prevent cardiac insufficiency. However, reperfusion itself may exacerbate cell death and myocardial injury, a process commonly referred to as ischemia/reperfusion (I/R) injury, which primarily involves cardiomyocytes and cardiac microvascular endothelial cells (CMECs) and is characterized by myocardial stunning, microvascular damage (MVD), reperfusion arrhythmia, and lethal reperfusion injury. MVD caused by I/R has been a neglected problem compared to myocardial injury. Clinically, the incidence of microvascular angina and/or no-reflow due to ineffective coronary perfusion accounts for 5-50% in patients after acute revascularization. MVD limiting drug diffusion into injured myocardium, is strongly associated with the development of heart failure. CMECs account for > 60% of the cardiac cellular components, and their role in myocardial I/R injury cannot be ignored. There are many studies on microvascular obstruction, but few studies on microvascular leakage, which may be mainly due to the lack of corresponding detection methods. In this review, we summarize the clinical manifestations, related mechanisms of MVD during myocardial I/R, laboratory and clinical examination means, as well as the research progress on potential therapies for MVD in recent years. Better understanding the characteristics and risk factors of MVD in patients after hemodynamic reconstruction is of great significance for managing MVD, preventing heart failure and improving patient prognosis.

What do we know about platelets in myocardial ischemia-reperfusion injury and why is it important?

Myocardial ischemia-reperfusion injury (MIRI), the joint result of ischemic injury and reperfusion injury, is associated with poor outcomes in patients with acute myocardial infarction undergoing primary percutaneous coronary intervention. Accumulating evidence demonstrates that activated platelets directly contribute to the pathogenesis of MIRI through participating in the formation of microthrombi, interaction with leukocytes, secretion of active substances, constriction of microvasculature, and activation of spinal afferent nerves. The molecular mechanisms underlying the above detrimental effects of activated platelets include the homotypic and heterotypic interactions through surface receptors, transduction of intracellular signals, and secretion of active substances. Revealing the roles of platelet activation in MIRI and the associated mechanisms would provide potential targets/strategies for the clinical evaluation and treatment of MIRI. Further studies are needed to characterize the temporal (ischemia phase vs. reperfusion phase) and spatial (systemic vs. local) distributions of platelet activation in MIRI by multi-omics strategies. To improve the likelihood of translating novel cardioprotective interventions into clinical practice, basic researches maximally replicating the complexity of clinical scenarios would be necessary.

Significance of mild thrombocytopenia in maintenance hemodialysis patients; a retrospective cohort study

Platelet activation in the hemodialysis (HD) circuit often causes thrombocytopenia. However, its clinical and pathophysiological significance has rarely been explored. Herein, we investigated the predictive value of thrombocytopenia for cardiovascular events (CVE) in maintenance HD patients and attempted to explore its mechanistic background considering recent knowledge of platelet dynamics. We conducted a retrospective cohort study on HD patients with the composite primary endpoint of predicting CVE, i.e., myocardial infarction, ischemic stroke, and cardiovascular death. Baseline clinical data were analyzed and explored. Multivariate Cox regression analysis showed that platelet decrease was independently associated with CVE. Thrombocytopenia was correlated with the disuse of antiplatelet therapy (APT) and macrocytosis. These findings are possibly associated with platelet activation and senescent hematopoiesis. The prognostic significance of thrombocytopenia was more prominent in patients undergoing APT, implying the presence of APT-resistant platelets in such patients. To fully explain these results, we hypothesized that HD-activated platelets induce the biological aging of hematopoiesis, which is presumably extramedullary in the lung, where activated platelets could deliver massive amounts of inflammatory cytokines and reactive oxidative species. This results in the production of qualitatively altered and hyper-reactive platelets, a process that could form a vicious cycle that induces CVE-associated thrombocytopenia. Further investigations focusing on the dynamics of the biological aging of platelets in HD patients are warranted.

Sympatho-adrenergic mechanisms in heart failure: new insights into pathophysiology

The sympathetic nervous system is activated in the setting of heart failure (HF) to compensate for hemodynamic instability. However, acute sympathetic surge or sustained high neuronal firing rates activates β-adrenergic receptor (βAR) signaling contributing to myocardial remodeling, dysfunction and electrical instability. Thus, sympatho-βAR activation is regarded as a hallmark of HF and forms pathophysiological basis for β-blocking therapy. Building upon earlier research findings, studies conducted in the recent decades have significantly advanced our understanding on the sympatho-adrenergic mechanism in HF, which forms the focus of this article. This review notes recent research progress regarding the roles of cardiac β2AR or α1AR in the failing heart, significance of β1AR-autoantibodies, and βAR signaling through G-protein independent signaling pathways. Sympatho-βAR regulation of immune cells or fibroblasts is specifically discussed. On the neuronal aspects, knowledge is assembled on the remodeling of sympathetic nerves of the failing heart, regulation by presynaptic α2AR of NE release, and findings on device-based neuromodulation of the sympathetic nervous system. The review ends with highlighting areas where significant knowledge gaps exist but hold promise for new breakthroughs.

Association Between Low-Density Lipoprotein Cholesterol and Platelet Distribution Width in Acute Ischemic Stroke

Objective: Elevated low-density lipoprotein cholesterol (LDL-C) is an established risk factor for ischemic stroke; however, whether LDL-C affects the platelet deformation function in the peripheral blood circulation in patients with acute ischemic stroke (AIS) is unknown. The present study aimed to investigate the relationship between LDL-C and platelet distribution width (PDW) in AIS patients. Methods: We conducted a cross-sectional hospitalized-based study of consecutive 438 patients with AIS within 24 h. Blood samples were collected upon admission and prior to drug administration, and LDL-C and PDW (a parameter that reflects the heterogeneity of platelet volume) were assessed. The relationship between LDL-C and PDW were analyzed by linear curve fitting analyses. Crude and adjusted beta coefficients of LDL-C for PDW with 95% confidence intervals were analyzed using multivariate-adjusted linear regression models. Results: The PDW was significantly higher in the high LDL-C group compared with those in the normal LDL-C group (16.28 ± 0.37 fl vs. 16.08 ± 0.37 fl, p < 0.001). Adjusted smoothed plots suggested that there are linear relationships between LDL-C and PDW, and the Pearson's correlation coefficient (95%) was 0.387 (0.304-0.464, p < 0.001). The beta coefficients (95% CI) between LDL-C and PDW were 0.15 (0.12-0.18, p < 0.001) and 0.14 (0.11-0.18, p < 0.001), respectively, in AIS patients before and after adjusting for potential confounders. Conclusion: Our study suggested that the elevated LDL-C level was related to increased PDW among AIS patients.

Mean platelet volume and coronary artery disease

PURPOSE OF REVIEW

To critically review the literature describing links between mean platelet volume (MPV) and cardiovascular disease (CVD). We will focus on coronary artery disease (CAD). The MPV is measured routinely as part of a routine blood count.

RECENT FINDINGS

There is accumulating evidence showing that the MPV may predict CVD, as well as outcomes in patients with CAD. There is also evidence linking MPV and comorbidities (e.g. diabetes mellitus and impaired glycaemic control) that are expected in patients with CAD. The effect on MPV of drugs commonly used to treat CAD has not been clarified, but there is some evidence that they may exert a beneficial effect on the MPV. More specifically, the MPV may predict the effect of antiplatelet drugs (e.g. clopidogrel). There is also evidence relating MPV to stroke, atrial fibrillation, coronary artery ectasia and periprocedural outcomes after percutaneous coronary intervention (PCI).

SUMMARY

Measuring the MPV may prove useful in CVD risk assessment in patients with established CAD or at risk of developing CAD. Overall, there is evidence pointing to the role of MPV as a contributor rather than simple marker of CVD.

Platelet phenotype and function in the absence of splenic sequestration (Review)

The spleen, in addition to its role in immunity, plays key roles in erythrocyte maintenance and platelet sequestration. Loss of the spleen via splenectomy occurs in approximately 6.4 to 7.1 per 100 000 people per year globally, commonly as a life-saving emergency procedure in trauma and a therapeutic procedure in hematological and hematological malignant conditions. It is associated with increased risk of life-threatening infection and thromboembolism, presumably via loss of splenic function, but the underlying mechanisms behind post-splenectomy thromboembolism are unclear. The splenectomized individual has a two-fold risk of thromboembolism as compared to non-splenectomized individuals and the risk of thromboembolism is elevated both post-operatively and in the longer term. Although those splenectomized for hematological conditions or hematological malignant conditions are at highest risk for thromboembolism, an increase in thromboembolic outcomes is also observed amongst individuals splenectomized for trauma, suggesting underlying disease state is only a partial factor. Although the physiological role of the splenic platelet pool on platelets is unclear, platelet changes after splenectomy suggest that the spleen may play a role in maintaining platelet quality and function. In hypersplenic conditions, sequestration can increase to sequester up to 72% of the total platelet mass. Following splenectomy, a thrombocytosis is commonly seen secondary to the loss of the ability to sequester platelets. Abnormal platelet quality and function have been observed as a consequence of splenectomy. These platelet defects seen after splenectomy may likely contribute to the increase in post-splenectomy thromboembolism. Here we draw upon the literature to characterize the post-splenectomy platelet and its potential role in post-splenectomy thromboembolism.

Inhibition of Platelets by Clopidogrel Suppressed Ang II-Induced Vascular Inflammation, Oxidative Stress, and Remodeling

Background

Platelets play a role in promoting inflammatory responses under several disease conditions. Platelets are activated in hypertensive patients. However, the mechanisms responsible for platelet‐mediating vascular inflammation are unknown. The present study investigated the role of platelets in promoting vascular inflammation following angiotensin II (Ang II) stimulation, and the efficacy of antiplatelet intervention.

Methods and Results

Within a mouse model of Ang II infusion (490 ng/kg per min), we measured the portion of P‐selectin–positive platelets and platelet‐monocyte (P‐M) binding in blood samples, and platelet accumulation and P‐M binding in vessels under Ang II stimulation at days 1, 3, and 7. We tested the efficacy of clopidogrel (15 mg/kg per day, followed by 5 mg/kg per day) on Ang II‐induced platelet activation, P‐M binding, vascular platelet accumulation, as well as vascular inflammation and remodeling at day 7 or 14. Clopidogrel reduced platelet vascular deposition (28.7±2.4% versus 18.3±2.9%), suppressed inflammatory cell infiltration (3.6±0.8×10⁴/vessel versus 2.3±1.2×10⁴/vessel) and oxidative stress, and attenuated vascular remodeling and dysfunction (55.0±5.5% versus 84.0±6.0%) following Ang II stimulation at day 7 or 14. Clopidogrel suppressed Ang II‐induced P‐M binding both at circulating (13.4±3.3% versus 5.9±2.7%) and regional (33.4±4.3% versus 11.9±2.7%) levels.

Conclusions

Platelets play a critical role in vascular inflammation under Ang II stimulation, with a marked promotion of P‐M binding as an important mechanism. Clopidogrel prevented vascular inflammation in Ang II‐infused mice.

Relaxin mitigates microvascular damage and inflammation following cardiac ischemia-reperfusion

Microvascular obstruction (MVO) and leakage (MVL) forms a pivotal part of microvascular damage following cardiac ischemia-reperfusion (IR). We tested the effect of relaxin therapy on MVO and MVL in mice following cardiac IR injury including severity of MVO and MVL, opening capillaries, infarct size, regional inflammation, cardiac function and remodelling, and permeability of cultured endothelial monolayer. Compared to vehicle group, relaxin treatment (50 μg/kg) reduced no-reflow area by 38% and the content of Evans blue as a permeability tracer by 56% in jeopardized myocardium (both P < 0.05), effects associated with increased opening capillaries. Relaxin also decreased leukocyte density, gene expression of cytokines, and mitigated IR-induced decrease in protein content of VE-cadherin and relaxin receptor. Infarct size was comparable between the two groups. At 2 weeks post-IR, relaxin treatment partially preserved cardiac contractile function and limited chamber dilatation versus untreated controls by echocardiography. Endothelial cell permeability assay demonstrated that relaxin attenuated leakage induced by hypoxia-reoxygenation, H₂O₂, or cytokines, action that was independent of nitric oxide but associated with the preservation of VE-cadherin. In conclusion, relaxin therapy attenuates IR-induced MVO and MVL and endothelial leakage. This protection was associated with reduced regional inflammatory responses and consequently led to alleviated adverse cardiac remodeling.

Platelets in cardiac ischaemia/reperfusion injury: a promising therapeutic target

Acute myocardial infarction (AMI) is the single leading cause of mortality and morbidity worldwide. A key component of AMI therapy is the timely reopening of occluded vessels to prevent further ischaemic damage to the myocardium. However, reperfusion of the ischaemic myocardium can itself trigger reperfusion injury causing up to 50% of the overall infarct size. In recent years, considerable research has been devoted to understanding the pathogenesis of ischaemia/reperfusion (I/R) injury and platelets have emerged as a major contributing factor. This review summarizes the role of platelets in the pathogenesis of I/R injury and highlights the potential of platelet-directed therapeutics to minimize cardiac I/R injury. Activated platelets infiltrate specifically into the ischaemic/reperfused myocardium and contribute to I/R injury by the formation of microthrombi, enhanced platelet-leucocyte aggregation, and the release of potent vasoconstrictor and pro-inflammatory molecules. This review demonstrates the benefits of platelet inhibition beyond their well-described anti-thrombotic effect and highlights the direct cardioprotective role of anti-platelet drugs. In particular, the inhibition of COX, the P2Y12 receptor and the GPIIb/IIIa receptor has demonstrated the potential to attenuate I/R injury. Moreover, targeting of drug candidates or regenerative cells to the activated platelets accumulated within the ischaemic/reperfused myocardium shows remarkable potential to protect the myocardium from I/R injury. Overall, activated platelets play a key role in the pathogenesis of I/R injury. Their direct inhibition as well as their use as epitopes for site-directed therapy is a unique and promising therapeutic approach for the prevention of I/R injury and ultimately the preservation of cardiac function.

Platelet-derived β2M regulates monocyte inflammatory responses

β-2 Microglobulin (β2M) is a molecular chaperone for the major histocompatibility class I (MHC I) complex, hemochromatosis factor protein (HFE), and the neonatal Fc receptor (FcRn), but β2M may also have less understood chaperone-independent functions. Elevated plasma β2M has a direct role in neurocognitive decline and is a risk factor for adverse cardiovascular events. β2M mRNA is present in platelets at very high levels, and β2M is part of the activated platelet releasate. In addition to their more well-studied thrombotic functions, platelets are important immune regulatory cells that release inflammatory molecules and contribute to leukocyte trafficking, activation, and differentiation. We have now found that platelet-derived β2M is a mediator of monocyte proinflammatory differentiation through noncanonical TGFβ receptor signaling. Circulating monocytes from mice lacking β2M only in platelets (Plt-β2M-/-) had a more proreparative monocyte phenotype, in part dependent on increased platelet-derived TGFβ signaling in the absence of β2M. Using a mouse myocardial infarction (MI) model, Plt-β2M-/- mice had limited post-MI proinflammatory monocyte responses and, instead, demonstrated early proreparative monocyte differentiation, profibrotic myofibroblast responses, and a rapid decline in heart function compared with WT mice. These data demonstrate a potentially novel chaperone-independent, monocyte phenotype-regulatory function for platelet β2M and that platelet-derived 2M and TGFβ have opposing roles in monocyte differentiation that may be important in tissue injury responses.

Prognostic value of rising mean platelet volume during hospitalization in patients with ST-segment elevation myocardial infarction treated with primary percutaneous coronary intervention

Background

The prognostic significance of changes in mean platelet volume (MPV) during hospitalization in ST segment elevation myocardial infarction (STEMI) patients underwent primary percutaneous coronary intervention (pPCI) has not been previously evaluated. The aim of this study was to determine the association of in-hospital changes in MPV and mortality in these patients.

Methods

Four hundred eighty consecutive STEMI patients were enrolled in this retrospective study. The patients were grouped as survivors (n = 370) or non-survivors (n = 110). MPV at admission, and at 48–72 h was evaluated. Change in MPV (MPV at 48–72 h minus MPV on admission) was defined as ΔMPV.

Results

At follow-up, long-term mortality was 23%. The non-survivors had a high ΔMPV than survivors (0.37 (− 0.1–0.89) vs 0.79 (0.30–1.40) fL, p <  0.001). A high ΔMPV was an independent predictor of all cause mortality ((HR: 1.301 [1.070–1.582], p = 0.008). Morever, for long-term mortality, the AUC of a multivariable model that included age, LVEF, Killip class, and history of stroke/TIA was 0.781 (95% CI:0.731–0.832, p <  0.001). When ΔMPV was added to a multivariable model, the AUC was 0.800 (95% CI: 0.750–0.848, z = 2.256, difference p = 0.0241, Fig. 1). Also, the addition of ΔMPV to a multivariable model was associated with a significant net reclassification improvement estimated at 24.5% (p = 0.027) and an integrated discrimination improvement of 0.014 (p = 0.0198).

Conclusions

Rising MPV during hospitalization in STEMI patients treated with pPCI was associated with long-term mortality.

Guidelines for experimental models of myocardial ischemia and infarction

Myocardial infarction is a prevalent major cardiovascular event that arises from myocardial ischemia with or without reperfusion, and basic and translational research is needed to better understand its underlying mechanisms and consequences for cardiac structure and function. Ischemia underlies a broad range of clinical scenarios ranging from angina to hibernation to permanent occlusion, and while reperfusion is mandatory for salvage from ischemic injury, reperfusion also inflicts injury on its own. In this consensus statement, we present recommendations for animal models of myocardial ischemia and infarction. With increasing awareness of the need for rigor and reproducibility in designing and performing scientific research to ensure validation of results, the goal of this review is to provide best practice information regarding myocardial ischemia-reperfusion and infarction models.

Listen to this article’s corresponding podcast at ajpheart.podbean.com/e/guidelines-for-experimental-models-of-myocardial-ischemia-and-infarction/.

Endogenous Annexin-A1 Regulates Haematopoietic Stem Cell Mobilisation and Inflammatory Response Post Myocardial Infarction in Mice In Vivo

Endogenous anti-inflammatory annexin-A1 (ANX-A1) plays an important role in preserving left ventricular (LV) viability and function after ischaemic insults in vitro, but its long-term cardioprotective actions in vivo are largely unknown. We tested the hypothesis that ANX-A1-deficiency exaggerates inflammation, haematopoietic stem progenitor cell (HSPC) activity and LV remodelling in response to myocardial ischaemia in vivo. Adult ANX-A1^−/− mice subjected to coronary artery occlusion exhibited increased infarct size and LV macrophage content after 24–48 h reperfusion compared with wildtype (WT) counterparts. In addition, ANX-A1^−/− mice exhibited greater expansion of HSPCs and altered pattern of HSPC mobilisation 8 days post-myocardial infarction, with increased circulating neutrophils and platelets, consistent with increased cardiac inflammation as a result of increased myeloid invading injured myocardium in response to MI. Furthermore, ANX-A1^−/− mice exhibited significantly increased expression of LV pro-inflammatory and pro-fibrotic genes and collagen deposition after MI compared to WT counterparts. ANX-A1-deficiency increased cardiac necrosis, inflammation, hypertrophy and fibrosis following MI, accompanied by exaggerated HSPC activity and impaired macrophage phenotype. These findings suggest that endogenous ANX-A1 regulates mobilisation and differentiation of HSPCs. Limiting excessive monocyte/neutrophil production may limit LV damage in vivo. Our findings support further development of novel ANX-A1-based therapies to improve cardiac outcomes after MI.

Significance of the thrombo-inflammatory status-based novel prognostic score as a useful predictor for in-hospital mortality of patients with type B acute aortic dissection

Background

Inflammation and thrombosis are associated with development and progression of acute aortic dissection (AAD). The aim of this study was to assess the prognostic significance of Simplified Thrombo-Inflammatory Prognostic Score (sTIPS), in patients with early phase type B AAD.

Methods

We retrospectively reviewed 491 patients with type B AAD between November 2012 and September 2015. sTIPS was calculated from the white blood cell count (WBC) and mean platelet volume to platelet count (MPV/PC) ratio, at the time of admission. Patients with both, WBC > 10 (10⁹/L) and MPV/PC ratio > 7.5 (10²fL/10⁹L^-1) were assigned a score of 2, while patients with high levels of either one or none of the above markers, were assigned scores of 1 and 0 respectively. Multivariable Cox regression analyses were used to investigate the associations between the score and hospital survival.

Results

Of the 491 type B AAD patients included in this analysis, 24 patients (4.9%) died during hospitalization. Kaplan-Meier analysis revealed that the cumulative mortality was significantly higher in patients with higher sTIPS (P = 0.001). Multivariable Cox regression analysis further indicated that higher sTIPS was a strong predictor of in-hospital mortality after eliminating all confounding factors (sTIPS 2: hazard ratio 4.704, 95%; confidence interval [CI] 1.184-18.685; P = 0.028; sTIPS 1: hazard ratio 1.918, 95%; CI 1.134-3.537; P = 0.045).

Conclusions

sTIPS at admission was a useful tool for stratifying the risk in type B AAD patients, for outcomes such as in-hospital mortality in the early phase.

Microvascular leakage in acute myocardial infarction: characterization by histology, biochemistry, and magnetic resonance imaging

Cardiac microvascular obstruction (MVO) after ischemia-reperfusion (I/R) has been well studied, but microvascular leakage (MVL) remains largely unexplored. We characterized MVL in the mouse I/R model by histology, biochemistry, and cardiac magnetic resonance (CMR) imaging. I/R was induced surgically in mice. MVL was determined by administrating the microvascular permeability tracer Evans blue (EB) and/or gadolinium-diethylenetriaminepentaacetic acid contrast. The size of MVL, infarction, and MVO in the heart was quantified histologically. Myocardial EB was extracted and quantified chromatographically. Serial CMR images were acquired from euthanized mice to determine late gadolinium enhancement (LGE) for comparison with MVL quantified by histology. I/R resulted in MVL with its severity dependent on the ischemic duration and reaching its maximum at 24–48 h after reperfusion. The size of MVL correlated with the degree of left ventricular dilatation and reduction in ejection fraction. Within the risk zone, the area of MVL (75 ± 2%) was greater than that of infarct (47 ± 4%, P < 0.01) or MVO (36 ± 4%, P < 0.01). Contour analysis of paired CMR-LGE by CMR and histological MVL images revealed a high degree of spatial colocalization ( r = 0.959, P < 0.0001). These data indicate that microvascular barrier function is damaged after I/R leading to MVL. Histological and biochemical means are able to characterize MVL by size and severity while CMR-LGE is a potential diagnostic tool for MVL. The size of ischemic myocardium exhibiting MVL was greater than that of infarction and MVO, implying a role of MVL in postinfarct pathophysiology.

NEW & NOTEWORTHY We characterized, for the first time, the features of microvascular leakage (MVL) as a consequence of reperfused myocardial infarction. The size of ischemic myocardium exhibiting MVL was significantly greater than that of infarction or no reflow. We made a proof-of-concept finding on the diagnostic potential of MVL by cardiac magnetic resonance imaging.