TP receptor activation and inhibition in atherothrombosis: the paradigm of diabetes mellitus

Emerging Roles and Therapeutic Applications of Arachidonic Acid Pathways in Cardiometabolic Diseases

Cardiometabolic disease has become a major health burden worldwide, with sharply increasing prevalence but highly limited therapeutic interventions. Emerging evidence has revealed that arachidonic acid derivatives and pathway factors link metabolic disorders to cardiovascular risks and intimately participate in the progression and severity of cardiometabolic diseases. In this review, we systemically summarized and updated the biological functions of arachidonic acid pathways in cardiometabolic diseases, mainly focusing on heart failure, hypertension, atherosclerosis, nonalcoholic fatty liver disease, obesity, and diabetes. We further discussed the cellular and molecular mechanisms of arachidonic acid pathway-mediated regulation of cardiometabolic diseases and highlighted the emerging clinical advances to improve these pathological conditions by targeting arachidonic acid metabolites and pathway factors.

Significance of urinary 11-dehydro-thromboxane B2 in age-related diseases: Focus on atherothrombosis

Platelet activation plays a key role in atherogenesis and atherothrombosis. Biochemical evidence of increased platelet activation in vivo can be reliably obtained through non-invasive measurement of thromboxane metabolite (TXM) excretion. Persistent biosynthesis of TXA₂ has been associated with several ageing-related diseases, including acute and chronic cardio-cerebrovascular diseases and cardiovascular risk factors, such as cigarette smoking, type 1 and type 2 diabetes mellitus, obesity, hypercholesterolemia, hyperhomocysteinemia, hypertension, chronic kidney disease, chronic inflammatory diseases. Given the systemic nature of TX excretion, involving predominantly platelet but also extraplatelet sources, urinary TXM may reflect either platelet cyclooxygenase-1 (COX-1)-dependent TX generation or COX-2-dependent biosynthesis by inflammatory cells and/or platelets, or a combination of the two, especially in clinical settings characterized by low-grade inflammation or enhanced platelet turnover. Although urinary 11-dehydro-TXB₂ levels are largely suppressed with low-dose aspirin, incomplete TXM suppression by aspirin predicts the future risk of vascular events and death in high-risk patients and may identify individuals who might benefit from treatments that more effectively block in vivo TX production or activity. Several disease-modifying agents, including lifestyle intervention, antidiabetic drugs and antiplatelet agents besides aspirin have been shown to reduce TX biosynthesis. Taken together, these aspects may contribute to the development of promising mechanism-based therapeutic strategies to reduce the progression of atherothrombosis. We intended to critically review current knowledge on both the pathophysiological significance of urinary TXM excretion in clinical settings related to ageing and atherothrombosis, as well as its prognostic value as a biomarker of vascular events.

A high glucose level is associated with decreased aspirin-mediated acetylation of platelet cyclooxygenase (COX)-1 at serine 529: A pilot study

Diabetes is a major risk factor for cardiovascular diseases. Although aspirin is considered a cornerstone of the prevention and treatment of atherothrombotic-related ischemic events, this antiplatelet drug appears to be less effective in patients with poorly controlled diabetes. It has been suggested that the glycation of platelet proteins plays a pivotal role in poor responsiveness to aspirin. However, a direct effect on the critical residue (serine 529, or Ser 529) of the catalytic pocket of cyclooxygenase 1 (COX-1) has never been demonstrated. This pilot study aimed to elucidate the impact of hyperglycaemia on aspirin acetylation of COX-1 using a targeted mass spectrometry approach. We observed that high glucose concentration had a direct impact on the level of acetylation of the COX-1 Ser 529 residue, whereas it's overall acetylation level remained unchanged. Moreover, the functional aspirin-induced inhibition of COX-1 was dose-dependently impaired as glucose concentrations increased. These in vitro findings were in line with data obtained using platelets from diabetic patients. These data provide new insights into the interplay between glucose and aspirin on platelet proteins and their effects on platelet COX-1. They also suggest a potential mechanistic explanation for the phenomenon of poor response to aspirin in diabetic patients. Data are available via ProteomeXchange with identifier PXD011204. SIGNIFICANCE: Deciphering the mutual interplay between glucose and aspirin-mediated acetylation on platelet COX-1, might be of great interest as there is still a lack of information of the mechanism underlying this process that may contribute to the less-than expected response of platelets to aspirin, often observed in diabetes.

Age-related increase of thromboxane B2 and risk of cardiovascular disease in atrial fibrillation

Aging is strictly associated with an increased incidence of cardiovascular events (CVEs) in the general population. Mechanisms underlying the risk of CVEs are still unclear. Platelet activation contributes to the onset of cardiovascular complications. The incidence of atrial fibrillation (AF) increases with age, and the natural history of AF is often complicated by CVEs. We prospectively investigated the relationship between age, urinary thromboxane (Tx) B₂, which reflects platelet activation, and CVEs in 833 AF patients. Median TxB₂ level was 120 [66-200] ng/mg of urinary creatinine. At multivariable linear regression analysis, age (B: 0.097, p=0.005) and previous MI/CHD (B: 0.069, p=0.047) were associated with log-TxB₂ levels. When we divided our population into age classes (i.e. < 60, 60-69, 70-79, ≥ 80 years), we found a significant difference in TxB₂ levels across classes (p=0.005), with a significant elevation at 74.6 years. During a mean follow-up of 40.9 months, 128 CVEs occurred; the rate of CVEs significantly increased with age classes (Log-rank test, p < 0.001). TxB₂ levels were higher in patients with, compared to those without, CVEs in patients aged 70-79 (p < 0.001) and ≥ 80 (p = 0.020) years. In conclusion, TxB₂ levels enhance by increasing age, suggesting that platelet activation contributes to CVEs in elderly patients with AF.

Atherothrombosis and Oxidative Stress: Mechanisms and Management in Elderly

SIGNIFICANCE

The incidence of cardiovascular events (CVEs) increases with age, representing the main cause of death in an elderly population. Aging is associated with overproduction of reactive oxygen species (ROS), which may affect clotting and platelet activation, and impair endothelial function, thus predisposing elderly patients to thrombotic complications. Recent Advances: There is increasing evidence to suggest that aging is associated with an imbalance between oxidative stress and antioxidant status. Thus, upregulation of ROS-producing enzymes such as nicotinamide adenine dinucleotide phosphate (NADPH) oxidase and myeloperoxidase, along with downregulation of antioxidant enzymes, such as superoxide dismutase and glutathione peroxidase, occurs during aging. This imbalance may predispose to thrombosis by enhancing platelet and clotting activation and eliciting endothelial dysfunction. Recently, gut-derived products, such as trimethylamine N-oxide (TMAO) and lipopolysaccharide, are emerging as novel atherosclerotic risk factors, and gut microbiota composition has been shown to change by aging, and may concur with the increased cardiovascular risk in the elderly.

CRITICAL ISSUES

Antioxidant treatment is ineffective in patients at risk or with cardiovascular disease. Further, anti-thrombotic treatment seems to work less in the elderly population.

FUTURE DIRECTIONS

Interventional trials with antioxidants targeting enzymes implicated in aging-related atherothrombosis are warranted to explore whether modulation of redox status is effective in lowering CVEs in the elderly. Antioxid. Redox Signal. 27, 1083-1124.

Urinary 11-dehydro-thromboxane B2 is associated with cardiovascular events and mortality in patients with atrial fibrillation

BACKGROUND

Patients with nonvalvular atrial fibrillation (AF) show high residual cardiovascular (CV) risk despite oral anticoagulants. Urinary 11-dehydro-thromboxane B2 (TxB2) is associated with an increased risk of CV events (CVEs), but its predictive value in patients with anticoagulated AF is unknown.

METHODS

A prospective single-center cohort study, including 837 patients with AF, was conducted. Mean time of follow-up was 30.0 months, yielding 2,062 person-years of observation. Urinary 11-dehydro-TxB2 was measured at baseline. The primary end point was the occurrence of a CVE including fatal/nonfatal myocardial infarction and ischemic stroke, transient ischemic attack, cardiac revascularization, and CV death.

RESULTS

Mean age of patients was 73.1 years, and 43.6% were women. Median 11-dehydro-TxB2 levels were 100 (interquartile range 50-187) ng/mg of urinary creatinine. Overall, the anticoagulation control was adequate (63.9% of mean time in therapeutic range). A CVE occurred in 99 (11.8%) patients, and 55 were CV deaths. At baseline, 11-dehydro-TxB2 levels were higher in patients with a CVE compared with those without (186 [107-400] vs 98 [52-170], P < .001). An increased rate of CVEs (log-rank test, P < .001) and CV deaths (P < .001) was observed across tertiles of 11-dehydro-TxB2. Cardiovascular events were associated with age (hazard ratios [HR] 1.72 per 1 SD, 95% CI 1.33-2.21, P < .001), diabetes mellitus (HR 1.89, 95% CI 1.20-2.96, P = .005), heart failure (HR 1.60, 95% CI 1.01-2.54, P = .044), history of stroke/transient ischemic attack (HR 1.96, 95% CI 1.25-3.06, P = .003), and 11-dehydro-TxB2 (HR 1.64 per 1 SD, 95% CI 1.42-1.89, P < .001).

CONCLUSIONS

Urinary 11-dehydro-TxB2 levels are associated with a residual risk of CVEs and CV mortality in patients with AF despite anticoagulant treatment.

Platelets and diabetes mellitus

Platelet activation plays a key role in atherothrombosis in type 2 diabetes mellitus (T2DM) and increased in vivo platelet activation with enhanced thromboxane (TX) biosynthesis has been reported in patients with impairment of glucose metabolism even in the earlier stages of disease and in the preclinical phases. In this regards, platelets appear as addresses and players carrying and transducing metabolic derangement into vascular injury. The present review critically addresses key pathophysiological aspects including (i) hyperglycemia, glycemic variability and insulin resistance as determinants and predictors of platelet activation, (ii) inflammatory mediators derived from platelets, such as soluble CD40 ligand, soluble CD36, Dickkopf-1 and probably soluble receptor for advanced glycation-end-products (sRAGE), which expand the functional repertoire of platelets from players of hemostasis and thrombosis to powerful amplifiers of inflammation by promoting the release of cytokines and chemokines, cell activation, and cell-cell interactions; (iii) molecular mechanisms underpinning the less-than-expected antithrombotic protection by aspirin (ASA), despite regular antiplatelet prophylaxis at the standard dosing regimen, and (iv) stratification of patients deserving different antiplatelet strategies, based on the metabolic phenotype. Taken together, these pathophysiological aspects may contribute to the development of promising mechanism-based therapeutic strategies to reduce the progression of atherothrombosis in diabetic subjects.

Low dose of acetylsalicylic acid and oxidative stress-mediated endothelial dysfunction in diabetes: a short-term evaluation

Current guidelines suggest the use of low doses of acetylsalicylic acid (ASA) for patients with diabetes mellitus (DM) in primary prevention. However, the evidences demonstrating the beneficial effect of ASA in primary prevention are conflicting. In this pilot study, we evaluated in a group of diabetic patients, in primary prevention, the impact of ASA treatment on oxidative stress and vascular function. We enrolled 22 newly diagnosed diabetic patients, without any previous clinical evidence of cardiovascular disease, to receive, in primary prevention, ASA (100 mg/daily). We tested, in basal condition, after 4 weeks of ASA administration and after 4 weeks of pharmacological washout, the impact of ASA treatment on endothelial function, assessed by a semipletysmographic method, measuring the main oxidative stress parameters related to it. As expected, after 4 weeks of treatment, ASA induced a significant reduction of plasma thromboxane-A2, as a consequence of cyclooxygenase-1 inhibition. By contrast, ASA significantly increased the plasma and urine 8-iso-PGF2α, a well-known prothrombotic molecule, parallel to an increase of plasma NOX2 levels. The enhancement of this oxidative pathway is associated with a significant impairment of endothelial vasodilation, assessed by reactive hyperemia index (RHI). The pharmacological washout reverted all parameters to basal condition. Our findings suggest that ASA utilization for primary prevention in diabetic patients causes a significant increase of oxidative stress burden impairing the vascular function. Present data, if confirmed on a larger population, could permanently discourage the use of the ASA for the primary prevention in patients with DM.

Oxidative stress-related mechanisms affecting response to aspirin in diabetes mellitus

Type 2 diabetes mellitus (T2DM) is a major cardiovascular risk factor. Persistent platelet activation plays a key role in atherothrombosis in T2DM. However, current antiplatelet treatments appear less effective in T2DM patients vs nondiabetics at similar risk. A large body of evidence supports the contention that oxidative stress, which characterizes DM, may be responsible, at least in part, for less-than-expected response to aspirin, with multiple mechanisms acting at several levels. This review discusses the pathophysiological mechanisms related to oxidative stress and contributing to suboptimal aspirin action or responsiveness. These include: (1) mechanisms counteracting the antiplatelet effect of aspirin, such as reduced platelet sensitivity to the antiaggregating effects of NO, due to high-glucose-mediated oxidative stress; (2) mechanisms interfering with COX acetylation especially at the platelet level, e.g., lipid hydroperoxide-dependent impaired acetylating effects of aspirin; (3) mechanisms favoring platelet priming (lipid hydroperoxides) or activation (F2-isoprostanes, acting as partial agonists of thromboxane receptor), or aldose-reductase pathway-mediated oxidative stress, leading to enhanced platelet thromboxane A2 generation or thromboxane receptor activation; (4) mechanisms favoring platelet recruitment, such as aspirin-induced platelet isoprostane formation; (5) modulation of megakaryocyte generation and thrombopoiesis by oxidative HO-1 inhibition; and (6) aspirin-iron interactions, eventually resulting in impaired pharmacological activity of aspirin, lipoperoxide burden, and enhanced generation of hydroxyl radicals capable of promoting protein kinase C activation and platelet aggregation. Acknowledgment of oxidative stress as a major contributor, not only of vascular complications, but also of suboptimal response to antiplatelet agents in T2DM, may open the way to designing and testing novel antithrombotic strategies, specifically targeting oxidative stress-mediated mechanisms of less-than-expected response to aspirin.

Circulating myeloid-related protein-8/14 is related to thromboxane-dependent platelet activation in patients with acute coronary syndrome, with and without ongoing low-dose aspirin treatment

BACKGROUND

Platelet activation is involved in acute coronary syndromes (ACS). Incomplete suppression by low-dose aspirin treatment of thromboxane (TX) metabolite excretion (urinary 11-dehydro-TXB2) is predictive of vascular events in high-risk patients. Myeloid-related protein (MRP)-8/14 is a heterodimer secreted on activation of platelets, monocytes, and neutrophils, regulating inflammation and predicting cardiovascular events. Among platelet transcripts, MRP-14 has emerged as a powerful predictor of ACS.

METHODS AND RESULTS

We enrolled 68 stable ischemic heart disease (IHD) and 63 ACS patients, undergoing coronary angiography, to evaluate whether MRP-8/14 release in the circulation is related to TX-dependent platelet activation in ACS and IHD patients and to residual TX biosynthesis in low-dose aspirin-treated ACS patients. In ACS patients, plasma MRP-8/14 and urinary 11-dehydro-TXB2 levels were linearly correlated (r=0.651, P<0.001) but significantly higher than those in IHD patients (P=0.012, P=0.044) only among subjects not receiving aspirin. In aspirin-treated ACS patients, MRP-8/14 and 11-dehydro-TXB2 were lower versus those not receiving aspirin (P<0.001) and still significantly correlated (r=0.528, P<0.001). Higher 11-dehydro-TXB2 significantly predicted higher MRP-8/14 in both all ACS patients and ACS receiving aspirin (P<0.001, adj R(2)=0.463 and adj R(2)=0.497) after multivariable adjustment. Conversely, plasma MRP-8/14 (P<0.001) and higher urinary 8-iso-prostaglandin F2α (P=0.050) levels were significant predictors of residual, on-aspirin, TX biosynthesis in ACS (adjusted R(2)=0.384).

CONCLUSIONS

Circulating MRP-8/14 is associated with TX-dependent platelet activation in ACS, even during low-dose aspirin treatment, suggesting a contribution of residual TX to MRP-8/14 shedding, which may further amplify platelet activation. Circulating MRP-8/14 may be a target to test different antiplatelet strategies in ACS.

Impact of vascular thromboxane prostanoid receptor activation on hemostasis, thrombosis, oxidative stress, and inflammation

The activation of thromboxane prostanoid (TP) receptor on platelets, monocytes/macrophages, endothelial cells, and vascular smooth muscle cells (SMC) plays important roles in regulating platelet activation and vascular tone and in the pathogenesis of thrombosis and vascular inflammation. Oxidative stress and vascular inflammation increase the formation of TP receptor agonists, which promote initiation and progression of atherogenesis and thrombosis. Furthermore, TP receptor activation promotes angiogenesis and vessel wall constriction. Besides thromboxane A₂ and its endoperoxide precursors, prostaglandin G₂ and H₂, isoprostanes, and 20-hydroxyeicosatetraenoic acid also activate TP receptor as autocrine or paracrine ligands. These additional TP activators play a role in pathological conditions such as diabetes, obesity, and hypertension, and their biosynthesis is not inhibited by aspirin, at variance with that of thromboxane A₂. The understanding of TP receptor function increased our current knowledge of the pathogenesis of atherosclerosis and thrombosis, highlighting the great impact that this receptor has in cardiovascular disorders.

An eicosanoid-centric view of atherothrombotic risk factors

Cardiovascular disease is the foremost cause of morbidity and mortality in the Western world. Atherosclerosis followed by thrombosis (atherothrombosis) is the pathological process underlying most myocardial, cerebral, and peripheral vascular events. Atherothrombosis is a complex and heterogeneous inflammatory process that involves interactions between many cell types (including vascular smooth muscle cells, endothelial cells, macrophages, and platelets) and processes (including migration, proliferation, and activation). Despite a wealth of knowledge from many recent studies using knockout mouse and human genetic studies (GWAS and candidate approach) identifying genes and proteins directly involved in these processes, traditional cardiovascular risk factors (hyperlipidemia, hypertension, smoking, diabetes mellitus, sex, and age) remain the most useful predictor of disease. Eicosanoids (20 carbon polyunsaturated fatty acid derivatives of arachidonic acid and other essential fatty acids) are emerging as important regulators of cardiovascular disease processes. Drugs indirectly modulating these signals, including COX-1/COX-2 inhibitors, have proven to play major roles in the atherothrombotic process. However, the complexity of their roles and regulation by opposing eicosanoid signaling, have contributed to the lack of therapies directed at the eicosanoid receptors themselves. This is likely to change, as our understanding of the structure, signaling, and function of the eicosanoid receptors improves. Indeed, a major advance is emerging from the characterization of dysfunctional naturally occurring mutations of the eicosanoid receptors. In light of the proven and continuing importance of risk factors, we have elected to focus on the relationship between eicosanoids and cardiovascular risk factors.

Variability in the response to antiplatelet treatment in diabetes mellitus

Atherothrombosis is a leading cause of death in patients with diabetes mellitus. Among factors contributing to the diabetic prothrombotic state, platelet activation plays a pivotal role. Numerous studies have investigated the benefits of antiplatelet therapy for primary and secondary cardiovascular prevention in diabetic patients. However, there are limited evidences that low-dose aspirin may be effective in this clinical setting. Several disease-specific factors have been identified as potential determinants of aspirin treatment failure. In this review, the main determinants of interindividual variability in response to antiplatelet agents are discussed, with particular emphasis on the pharmacokinetic and pharmacodynamic mechanisms of clinical efficacy and safety of antiplatelet drugs in patients with diabetes mellitus.

Thromboxane receptors antagonists and/or synthase inhibitors

Atherothrombosis is the major cause of mortality and morbidity in Western countries. Several clinical conditions are characterized by increased incidence of cardiovascular events and enhanced thromboxane (TX)-dependent platelet activation. Enhanced TX generation may be explained by mechanisms relatively insensitive to aspirin. More potent drugs possibly overcoming aspirin efficacy may be desirable. Thromboxane synthase inhibitors (TXSI) and thromboxane receptor antagonists (TXRA) have the potential to prove more effective than aspirin due to their different mechanism of action along the pathway of TXA(2). TXSI prevent the conversion of PGH(2) to TXA(2), reducing TXA(2) synthesis mainly in platelets, whereas TXRA block the downstream consequences of TXA(2) receptors (TP) activation.TXA(2) is a potent inducer of platelet activation through its interaction with TP on platelets. TP are activated not only by TXA(2), but also by prostaglandin (PG) D(2), PGE(2), PGF(2α), PGH(2), PG endoperoxides (i.e., 20-HETE), and isoprostanes, all representing aspirin-insensitive mechanisms of TP activation. Moreover, TP are also expressed on several cell types such as macrophages or monocytes, and vascular endothelial cells, and exert antiatherosclerotic, antivasoconstrictive, and antithrombotic effects, depending on the cellular target.Thus, targeting TP receptor, a common downstream pathway for both platelet and extraplatelet TXA(2) as well as for endoperoxides and isoprostanes, may be a useful antiatherosclerotic and a more powerful antithrombotic intervention in clinical settings, such as diabetes mellitus, characterized by persistently enhanced thromboxane (TX)-dependent platelet activation through isoprostane formation and low-grade inflammation, leading to extraplatelet sources of TXA(2). Among TXRA, terutroban is an orally active drug in clinical development for use in secondary prevention of thrombotic events in cardiovascular disease. Despite great expectations on this drug supported by a large body of preclinical and clinical evidence and pathophysiological rationale, the PERFORM trial failed to demonstrate the superiority of terutroban over aspirin in secondary prevention of cerebrovascular and cardiovascular events among ~20,000 patients with stroke. However, the clinical setting and the design of the study in which the drug has been challenged may explain, at least in part, this unexpected finding.Drugs with dual action, such as dual TXS inhibitors/TP antagonist and dual COXIB/TP antagonists are currently in clinical development. The theoretical rationale for their benefit and the ongoing clinical studies are herein discussed.

Platelet activation in obesity and metabolic syndrome

Obesity is associated with increased cardiovascular disease. Metabolic syndrome (MS) identifies substantial additional cardiovascular risk beyond the individual risk factors, and is a powerful predictor of cardiovascular events even regardless of body mass index, thus suggesting a common downstream pathway conferring increased cardiovascular risk. Platelet hyper-reactivity/activation plays a central role to accelerate atherothrombosis and is the result of the interaction among the features clustering in obesity and MS: insulin resistance, inflammation, oxidative stress, endothelial dysfunction. Interestingly, the same pathogenic events largely account for the less-than-expected response to antiplatelet agents, namely low-dose aspirin. The proposed explanations for this phenomenon, besides underdosing of drug and/or reduced bioavailability, subsequent to excess of adipose tissue, include enhanced platelet turnover, leading to unacetylated COX-1 and COX-2 in newly formed platelets as a source of aspirin-escaping thromboxane formation; extraplatelet sources of thromboxane, driven by inflammatory triggers; and enhanced lipid peroxidation, activating platelets with a mechanism bypassing COX-1 acetylation or limiting COX-isozyme acetylation by aspirin. This review will address the complex interactions between platelets and the pathogenic events occurring in obesity and MS, trying to translate this body of mechanistic information into a clinically relevant read-out, in order to establish novel strategies in the prevention/treatment of atherothrombosis.

Diabetes mellitus and thrombosis

Atherothrombosis is the leading cause of morbidity and mortality in patients with diabetes mellitus. Several mechanisms contribute to the diabetic prothrombotic state, including endothelial dysfunction, coagulative activation and platelet hyper-reactivity. In particular, diabetic platelets are characterised by dysregulation of several signaling pathways leading to enhanced adhesion, activation and aggregation. These alterations result from the interaction among hyperglycemia, insulin resistance, inflammation and oxidative stress. This review will provide an overview of the current status of knowledge on mechanisms of accelerated atherothrombosis in patients with diabetes mellitus.