Risk factor correlates of platelet and leukocyte markers assessed by flow cytometry in a population-based sample

Sex-specific differences in cytokine signaling pathways in circulating monocytes of cardiovascular disease patients

BACKGROUND AND AIMS

This study aims to identify sex-specific transcriptional differences and signaling pathways in circulating monocytes contributing to cardiovascular disease.

METHODS AND RESULTS

We generated sex-biased gene expression signatures by comparing male versus female monocytes of coronary artery disease (CAD) patients (n = 450) from the Center for Translational Molecular Medicine-Circulating Cells Cohort. Gene set enrichment analysis demonstrated that monocytes from female CAD patients carry stronger chemotaxis and migratory signature than those from males. We then inferred cytokine signaling activities based on CytoSig database of 51 cytokine and growth factor regulation profiles. Monocytes from females feature a higher activation level of EGF, IFN1, VEGF, GM-CSF, and CD40L pathways, whereas IL-4, INS, and HMGB1 signaling was seen to be more activated in males. These sex differences were not observed in healthy subjects, as shown for an independent monocyte cohort of healthy subjects (GSE56034, n = 485). More pronounced GM-CSF signaling in monocytes of female CAD patients was confirmed by the significant enrichment of GM-CSF-activated monocyte signature in females. As we show these effects were not due to increased plasma levels of the corresponding ligands, sex-intrinsic differences in monocyte signaling regulation are suggested. Consistently, regulatory network analysis revealed jun-B as a shared transcription factor activated in all female-specific pathways except IFN1 but suppressed in male-activated IL-4.

CONCLUSIONS

We observed overt CAD-specific sex differences in monocyte transcriptional profiles and cytokine- or growth factor-induced responses, which provide insights into underlying mechanisms of sex differences in CVD.

Sex hormones regulate metainflammation in diet-induced obesity in mice

Men have a statistically higher risk of metabolic and cardiovascular disease than premenopausal women, but the mechanisms mediating these differences are elusive. Chronic inflammation during obesity contributes to disease risk and is significantly more robust in males. Prior work demonstrated that compared with obese males, obese females have reduced proinflammatory adipose tissue macrophages (ATMs). Given the paucity of data on how sex hormones contribute to macrophage responses in obesity, we sought to understand the role of sex hormones in promoting obesity-induced myeloid inflammation. We used gonadectomy, estrogen receptor-deficient alpha chimeras, and androgen-insensitive mice to model sex hormone deficiency. These models were evaluated in diet-induced obesity conditions (high-fat diet [HFD]) and in vitro myeloid assays. We found that ovariectomy increased weight gain and adiposity. Ovariectomized females had increased ATMs and bone marrow myeloid colonies compared with sham-gonadectomized females. In addition, castrated males exposed to HFD had improved glucose tolerance, insulin sensitivity, and adiposity with fewer Ly6chi monocytes and bone marrow myeloid colonies compared with sham-gonadectomized males, although local adipose inflammation was enhanced. Similar findings were observed in androgen-insensitive mice; however, these mice had fewer CD11c+ ATMs, implying a developmental role for androgens in myelopoiesis and adipose inflammation. We concluded that gonadectomy results in convergence of metabolic and inflammatory responses to HFD between the sexes, and that myeloid estrogen receptor alpha contributes minimally to diet-induced inflammatory responses, whereas loss of androgen-receptor signaling improves metabolic and inflammatory outcomes. These studies demonstrate that sex hormones play a critical role in sex differences in obesity, metabolic dysfunction, and myeloid inflammation.

Platelet reactivity in response to aspirin and ticagrelor in African-Americans and European-Americans

Platelet gene polymorphisms are associated with variable on-treatment platelet reactivity and vary by race. Whether differences in platelet reactivity and aspirin or ticagrelor exist between African-American and European-Americans remains poorly understood. Biological samples from three prior prospective antiplatelet challenge studies at the Duke Clinical Research Unit were used to compare platelet reactivity between African-American and European-American subjects. Platelet reactivity at baseline, on-aspirin, on-ticagrelor, and the treatment effect of aspirin or ticagrelor were compared between groups using an adjusted mixed effects model. Compared with European-Americans (n = 282; 50% female; mean ± standard deviation age, 50 ± 16), African-Americans (n = 209; 67% female; age 48 ± 12) had lower baseline platelet reactivity with platelet function analyzer-100 (PFA-100) (p < 0.01) and with light transmission aggregometry (LTA) in response to arachidonic acid (AA), adenosine diphosphate (ADP), and epinephrine agonists (p < 0.05). African-Americans had lower platelet reactivity on aspirin in response to ADP, epinephrine, and collagen (p < 0.05) and on ticagrelor in response to AA, ADP, and collagen (p < 0.05). The treatment effect of aspirin was greater in European-Americans with an AA agonist (p = 0.002). Between-race differences with in vitro aspirin mirrored those seen in vivo. The treatment effect of ticagrelor was greater in European-Americans in response to ADP (p < 0.05) but with collagen, the treatment effect was greater for African-Americans (p < 0.05). Platelet reactivity was overall lower in African-Americans off-treatment, on aspirin, and on ticagrelor. European-Americans experienced greater platelet suppression on aspirin and on ticagrelor. The aspirin response difference in vivo and in vitro suggests a mechanism intrinsic to the platelet. Whether the absolute level of platelet reactivity or the degree of platelet suppression after treatment is more important for clinical outcomes is uncertain.

Ethnic Differences in Oral Antithrombotic Therapy

Oral antithrombotic therapy (antiplatelet therapy and anticoagulation therapy) is a key element of pharmacotherapy in patients with cardiovascular (CV) disease. Several reports of ethnic differences have suggested that there may be difference therapeutic requirements and response to therapy for antithrombotic therapy. In particular for East Asians, there seems to be a lower incidence of ischemic outcomes and a higher incidence of bleeding outcomes compared to Westerners. The purpose of this review is to describe the ethnicity-related differences in antithrombotic therapy for CV disease and to discuss the need to establish a more effective and targeted antithrombotic treatment strategy in East Asians.

Sex as a Biological Variable in Atherosclerosis

Atherosclerosis is a chronic inflammatory vascular disease and the predominant cause of heart attack and ischemic stroke. Despite the well-known sexual dimorphism in the incidence and complications of atherosclerosis, there are relatively limited data in the clinical and preclinical literature to rigorously address mechanisms underlying sex as a biological variable in atherosclerosis. In multiple histological and imaging studies, overall plaque burden and markers of inflammation appear to be greater in men than women and are predictive of cardiovascular events. However, while younger women are relatively protected from cardiovascular disease, by the seventh decade, the incidence of myocardial infarction in women ultimately surpasses that of men, suggesting an interaction between sex and age. Most preclinical studies in animal atherosclerosis models do not examine both sexes, and even in those that do, well-powered direct statistical comparisons for sex as an independent variable remain rare. This article reviews the available data. Overall, male animals appear to have more inflamed yet smaller plaques compared to female animals. Plaque inflammation is often used as a surrogate end point for plaque vulnerability in animals. The available data support the notion that rather than plaque size, plaque inflammation may be more relevant in assessing sex-specific mechanisms since the findings correlate with the sex difference in ischemic events and mortality and thus may be more reflective of the human condition. Overall, the number of preclinical studies directly comparing plaque inflammation between the sexes is extremely limited relative to the vast literature exploring atherosclerosis mechanisms. Failure to include both sexes and to address age in mechanistic atherosclerosis studies are missed opportunities to uncover underlying sex-specific mechanisms. Understanding the mechanisms driving sex as a biological variable in atherosclerotic disease is critical to future precision medicine strategies to mitigate what is still the leading cause of death of men and women worldwide.

Genetic and Nongenetic Implications of Racial Variation in Response to Antiplatelet Therapy

Race has been identified as an independent risk factor for poor prognosis and an independent predictor of survival in coronary artery disease. Race-related dissimilarities have been identified in cardiovascular patients in terms of age of presentation, co-morbidities, socioeconomic status, and treatment approach as well as genetically driven race-related disparities in responsiveness to medications. Antiplatelet therapy represents a fundamental component of therapy in cardiovascular patients, especially in patients presenting with acute coronary syndromes. It has been argued that the different level of platelet reactivity and varying response to antiplatelet therapy among races may account in part for worse outcomes in certain populations. The purpose of this review is to describe genotypic and phenotypic race-related differences in platelet reactivity and responsiveness to cardiovascular treatment, focusing on antiplatelet therapy to highlight the need establish a more effective and targeted antithrombotic strategy.

Circulating monocyte-platelet aggregates are a robust marker of platelet activity in cardiovascular disease

BACKGROUND AND AIMS

Platelets are a major culprit in the pathogenesis of cardiovascular disease (CVD). Circulating monocyte-platelet aggregates (MPA) represent the crossroads between atherothrombosis and inflammation. However, there is little understanding of the platelets and monocytes that comprise MPA and the prevalence of MPA in different CVD phenotypes. We aimed to establish (1) the reproducibility of MPA over time in circulating blood samples from healthy controls, (2) the effect of aspirin, (3) the relationship between MPA and platelet activity and monocyte subtype, and (4) the association between MPA and CVD phenotype (coronary artery disease, peripheral artery disease [PAD], abdominal aortic aneurysm, and carotid artery stenosis).

METHODS AND RESULTS

MPA were identified by CD14⁺ monocytes positive for CD61⁺ platelets in healthy subjects and in patients with CVD. We found that MPA did not significantly differ over time in healthy controls, nor altered by aspirin use. Compared with healthy controls, MPA were significantly higher in CVD (9.4% [8.2, 11.1] vs. 21.8% [11.5, 44.1], p < 0.001) which remained significant after multivariable adjustment (β = 9.1 [SER = 3.9], p = 0.02). We found PAD to be associated with a higher MPA in circulation (β = 19.3 [SER = 6.0], p = 0.001), and among PAD subjects, MPA was higher in subjects with critical limb ischemia (34.9% [21.9, 51.15] vs. 21.6% [15.1, 40.6], p = 0.0015), and significance remained following multivariable adjustment (β = 14.77 (SE = 4.35), p = 0.001).

CONCLUSIONS

Circulating MPA are a robust marker of platelet activity and monocyte inflammation, unaffected by low-dose aspirin, and are significantly elevated in subjects with CVD, particularly those with PAD.

Changes in Blood Factors and Ultrasound Findings in Mild Cognitive Impairment and Dementia

The present study aimed to assess the changes in blood factors and ultrasound measures of atherosclerosis burden patient with mild cognitive impairment (MCI) and dementia. Peripheral blood samples and ultrasonography findings were obtained for 53 enrolled participants. Flow cytometry was used to evaluate levels of activated platelets and platelet-leukocyte aggregates (PLAs). The number of platelets expressing p-selectin was correlated with intima media thickness (IMT) and plaque number in both the MCI and dementia groups. The number of platelets expressing p-selectin glycoprotein ligand (PSGL) was strongly correlated with IMT in patients with MCI, whereas the number of platelets expressing PGSL was correlated with plaque number rather than IMT in patients with dementia. PLAs was associated with both IMT and plaque number in patients with MCI but not in those with dementia. Our findings demonstrate that alterations in IMT and plaque number are associated with an increased risk of cognitive decline as well as conversion from MCI to dementia and that blood factor analysis may aid to detect the severity of cognitive decline.

The Role of Sex and Sex Hormones in Regulating Obesity-Induced Inflammation

Metabolic and non-metabolic complications due to obesity are becoming more prevalent, yet our understanding of the mechanisms driving these is not. This is due to individual risk factor variability making it difficult to predict disease outcomes such as diabetes and insulin resistance. Gender is a critical factor in obesity outcomes with women having more adiposity but reduced metabolic complications compared to men. The role of immune system activation during obesity is an emerging field that links adiposity to metabolic syndrome. Furthermore, evidence from animal models suggests that sex differences exist in immune responses and, therefore, could be a possible mechanism leading to sex differences in metabolic disease. While there is still much to learn in the area of sex-differences research, this chapter will review the current knowledge and literature detailing the role of sex and sex hormones on adiposity and metabolically induced inflammation in obesity.

Influence of race and sex on thrombogenicity in a large cohort of coronary artery disease patients

Background

It is uncertain whether sex and race affect thrombogenicity in patients with coronary artery disease. We evaluated the effects of sex and race on thrombogenicity in patients with coronary artery disease treated with aspirin.

Methods and Results

Patients on aspirin therapy for 1 week or longer with known or suspected coronary artery disease undergoing nonurgent cardiac catheterization (n=1172), of whom 924 were on aspirin and clopidogrel therapy, were studied. The primary end point was thrombin‐induced platelet‐fibrin clot strength (MA_KH) measured by thrombelastography. Secondary end points included coagulation index, a measure of overall coagulation; G, another measure of clot strength; and maximal platelet aggregation. Women had greater MA_KH, G, and coagulation index than men, both with and without clopidogrel therapy (with clopidogrel: 68.3±6 versus 65.8±6 mm, P<0.0001; 11.4±3 versus 9.5±4 dyne/cm², P<0.0001; and 0.12±3 versus −0.7±3, P=0.003, respectively). Platelet aggregation (induced by ADP, thrombin receptor activating peptide, or collagen) did not differ between sexes. Black patients had greater MA_KH and G than white patients (with clopidogrel: 67.8±7 versus 66.4±6 mm, P=0.005; 11±4 versus 10±3 dyne/cm², P=0.02, respectively). Black women had the highest MA_KH levels. By multivariate analysis, sex, race, diabetes, platelet count, and hemoglobin level were independently associated with MA_KH. Sex, but not race, was also associated with the frequency of MA_KH ≥72 mm (a threshold related to ischemic event occurrence in patients undergoing coronary intervention).

Conclusions

Sex and race independently influence platelet‐fibrin clot strength. Black women appear to have the highest thrombogenicity profile, potentially conferring a high‐risk phenotype for thrombotic event occurrence.

The ARIC carotid MRI study of blood cellular markers: an inverse association of monocyte myeloperoxidase content with peripheral arterial disease

We evaluated the association of blood monocyte and platelet activation markers with the risk of peripheral artery disease (PAD) in a multicenter study of atherosclerosis among African American and Caucasian patients. Flow cytometric analysis of blood cells was performed in 1791 participants (209 cases with PAD and 1582 noncases) from the cross-sectional Atherosclerosis Risk in Communities Carotid Magnetic Resonance Imaging ([MRI] ARIC Carotid MRI) Study to assess platelet glycoproteins IIb and IIIa, P-selectin, CD40 ligand, platelet-leukocyte aggregates, monocyte lipopolysaccharide receptor, toll-like receptors (TLRs) 2 and 4, P-selectin glycoprotein ligand 1, cyclooxygenase 2, and myeloperoxidase. Multivariate regression analyses evaluated the association of cellular markers with the risk of PAD. After adjusting for age, race, and gender, platelet CD40L, and monocyte myeloperoxidase (mMPO) levels were significantly lower (P < .001), and monocyte TLR-4 levels were higher (P = .03) in patients with PAD. With additional adjustments for conventional risk factors, mMPO remained inversely and independently associated with the risk of PAD (odds ratio [OR]: 0.35, P = .01).

Genetic variants in TLR2 and TLR4 are associated with markers of monocyte activation: the Atherosclerosis Risk in Communities MRI Study

Markers of monocyte activation play a critical role in atherosclerosis, but little is known about the genetic influences on cellular levels. Therefore, we investigated the influence of genetic variants in monocyte differentiation antigen (CD14), toll-like receptor-4 (TLR4), toll-like receptor-2 (TLR2), and myeloperoxidase (MPO) on monocyte surface receptor levels. The study sample consisted of 1,817 members of a biracial cohort of adults from the Atherosclerosis Risk in Communities Carotid MRI Study. Monocyte receptors were measured using flow cytometry on fasting whole blood samples. TLR2 rs1816702 genotype was significantly associated with CD14+/TLR2+ percent of positive cells (%) and median fluorescence intensity (MFI) in whites but not in blacks (p < 0.001). Specifically, the presence of the minor T-allele was associated with increased receptor levels. In blacks, TLR4 rs5030719 was significantly associated with CD14+/TLR4+ monocytes (MFI) with mean ± SE intensities of 16.7 ± 0.05 and 16.0 ± 0.14 for GG and GT/TT genotypes, respectively (p < 0.001). Variants in TLR2 and TLR4 were associated with monocyte receptor levels of TLR2 and TLR4, respectively, in a biracial cohort of adults. To our knowledge, this is the first study to look at associations between variants in the toll-like receptor family and toll-like receptor levels on monocytes.

Association of blood monocyte and platelet markers with carotid artery characteristics: the atherosclerosis risk in communities carotid MRI study

BACKGROUND

Atherosclerosis is characterized by infiltration of inflammatory cells from circulating blood. Blood cell activation could play an important role in plaque formation.

METHODS

We analyzed the relationship between blood cellular markers and quantitative measures of carotid wall components in 1,546 participants from the ARIC (Atherosclerosis Risk in Communities) Carotid MRI Study. Carotid imaging was performed using a gadolinium contrast-enhanced MRI and cellular phenotyping by flow cytometry.

RESULTS

Monocyte Toll-like receptor (TLR)-2 is associated with larger plaques, while CD14, myeloperoxidase, and TLR-4 associate with smaller. Platelet CD40L is associated with smaller plaques and thinner caps, while P-selectin is associated with smaller core size.

CONCLUSIONS

Blood cell activation is significantly associated with atherosclerotic changes of the carotid wall.

Associations between dietary patterns and flow cytometry-measured biomarkers of inflammation and cellular activation in the Atherosclerosis Risk in Communities (ARIC) Carotid Artery MRI Study

BACKGROUND

Specific foods and overall dietary patterns are associated with soluble biomarkers of systemic inflammation and endothelial activation. However, no large epidemiological studies have evaluated relationships between such dietary factors and cell-specific markers of activation and inflammation as measured by flow cytometry.

METHODS

Cell aggregates and multiple platelet and leukocyte markers were quantified by flow cytometry in fresh whole blood from 1101 white adults participating in the Carotid Artery MRI Study, a subset of the larger Atherosclerosis Risk in Communities (ARIC) Study. Two dietary patterns ("Healthy" and "Western") were empirically derived via principal components analysis using data collected by food frequency questionnaire. Cross-sectional associations between dietary patterns and flow cytometry-measured biomarkers were evaluated, adjusting for demographics and lifestyle factors, including medications use.

RESULTS

After multivariable adjustment, monocyte lipopolysaccharide receptor (CD14), monocyte toll-like receptor-2, and platelet glycoprotein IIb (CD41) showed inverse associations with the Healthy dietary pattern (p=0.01, 0.04, and 0.01, respectively). In contrast, the Western dietary pattern was positively associated with CD41 and platelet-granulocyte aggregates (p=0.01 and 0.04, respectively). Independent of other dietary factors, alcohol consumption was inversely associated with levels of pan-leukocyte marker (CD45), P-selectin (CD62P) on PLA1 and on PLA2 platelets, and platelet-monocyte, platelet-granulocyte, and platelet-lymphocyte aggregates.

CONCLUSION

Dietary patterns and alcohol intake were each cross-sectionally associated with select markers of cellular activation and inflammation measured by flow cytometry. These data are consistent with the hypothesis that holistic measures of dietary intake are associated with inflammation.

Large-scale genomic studies reveal central role of ABO in sP-selectin and sICAM-1 levels

P-selectin and intercellular adhesion molecule-1 (ICAM-1) participate in inflammatory processes by promoting adhesion of leukocytes to vascular wall endothelium. Their soluble levels have been associated with adverse cardiovascular events. To identify loci affecting soluble levels of P-selectin (sP-selectin) and ICAM-1 (sICAM-1), we performed a genome-wide association study in a sample of 4115 (sP-selectin) and 9813 (sICAM-1) individuals of European ancestry as a part of The Cohorts for Heart and Aging Research in Genome Epidemiology consortium. The most significant SNP association for sP-selectin was within the SELP gene (rs6136, P = 4.05 x 10(-61)) and for sICAM-1 levels within the ICAM-1 gene (rs3093030, P = 3.53 x 10(-23)). Both sP-selectin and sICAM-1 were associated with ABO gene variants (rs579459, P = 1.86 x 10(-41) and rs649129, P = 1.22 x 10(-15), respectively) and in both cases the observed associations could be accounted for by the A1 allele of the ABO blood group. The absence of an association between ABO blood group and platelet-bound P-selectin levels in an independent subsample (N = 1088) from the ARIC study, suggests that the ABO blood group may influence cleavage of the P-selectin protein from the cell surface or clearance from the circulation, rather than its production and cellular presentation. These results provide new insights into adhesion molecule biology.