Improved integration of single-cell transcriptome data demonstrates common and unique signatures of heart failure in mice and humans

BACKGROUND

Cardiovascular research heavily relies on mouse (Mus musculus) models to study disease mechanisms and to test novel biomarkers and medications. Yet, applying these results to patients remains a major challenge and often results in noneffective drugs. Therefore, it is an open challenge of translational science to develop models with high similarities and predictive value. This requires a comparison of disease models in mice with diseased tissue derived from humans.

RESULTS

To compare the transcriptional signatures at single-cell resolution, we implemented an integration pipeline called OrthoIntegrate, which uniquely assigns orthologs and therewith merges single-cell RNA sequencing (scRNA-seq) RNA of different species. The pipeline has been designed to be as easy to use and is fully integrable in the standard Seurat workflow.We applied OrthoIntegrate on scRNA-seq from cardiac tissue of heart failure patients with reduced ejection fraction (HFrEF) and scRNA-seq from the mice after chronic infarction, which is a commonly used mouse model to mimic HFrEF. We discovered shared and distinct regulatory pathways between human HFrEF patients and the corresponding mouse model. Overall, 54% of genes were commonly regulated, including major changes in cardiomyocyte energy metabolism. However, several regulatory pathways (e.g., angiogenesis) were specifically regulated in humans.

CONCLUSIONS

The demonstration of unique pathways occurring in humans indicates limitations on the comparability between mice models and human HFrEF and shows that results from the mice model should be validated carefully. OrthoIntegrate is publicly accessible (https://github.com/MarianoRuzJurado/OrthoIntegrate) and can be used to integrate other large datasets to provide a general comparison of models with patient data.

Cardiomyocyte hyperplasia and immaturity but not hypertrophy are characteristic features of patients with RASopathies

AIMS

RASopathies are caused by mutations in genes that alter the MAP kinase pathway and are marked by several malformations with cardiovascular disorders as the predominant cause of mortality. Mechanistic insights in the underlying pathogenesis in affected cardiac tissue are rare. The aim of the study was to assess the impact of RASopathy causing mutations on the human heart.

METHODS AND RESULTS

Using single cell approaches and histopathology we analyzed cardiac tissue from children with different RASopathy-associated mutations compared to age-matched dilated cardiomyopathy (DCM) and control hearts. The volume of cardiomyocytes was reduced in RASopathy conditions compared to controls and DCM patients, and the estimated number of cardiomyocytes per heart was ~4-10 times higher. Single nuclei RNA sequencing of a 13-year-old RASopathy patient (carrying a PTPN11 c.1528C > G mutation) revealed that myocardial cell composition and transcriptional patterns were similar to <1 year old DCM hearts. Additionally, immaturity of cardiomyocytes is shown by an increased MYH6/MYH7 expression ratio and reduced expression of genes associated with fatty acid metabolism. In the patient with the PTPN11 mutation activation of the MAP kinase pathway was not evident in cardiomyocytes, whereas increased phosphorylation of PDK1 and its downstream kinase Akt was detected.

CONCLUSION

In conclusion, an immature cardiomyocyte differentiation status appears to be preserved in juvenile RASopathy patients. The increased mass of the heart in such patients is due to an increase in cardiomyocyte number (hyperplasia) but not an enlargement of individual cardiomyocytes (hypertrophy).

Acute injury to the mouse carotid artery provokes a distinct healing response

Treatment of vascular stenosis with angioplasty results in acute vascular damage, which may lead to restenosis. Owing to the highly complex cellularity of blood vessels, the healing response following this damage is incompletely understood. To gain further insight into this process, scRNA-seq of mouse carotid tissue after wire injury was performed. Stages of acute inflammation, resolution and remodeling were recapitulated in these data. To identify cell types which give rise to neointima, analyses focused on smooth muscle cell and fibroblast populations, and included data integration with scRNA-seq data from myocardial infarction and atherosclerosis datasets. Following carotid injury, a subpopulation of smooth muscle cells which also arises during atherosclerosis and myocardial infarction was identified. So-called stem cell/endothelial cell/monocyte (SEM) cells are candidates for repopulating injured vessels, and were amongst the most proliferative cell clusters following wire-injury of the carotid artery. Importantly, SEM cells exhibit specific transcriptional profiles which could be therapeutically targeted. SEM cell gene expression patterns could also be detected in bulk RNA-sequencing of neointimal tissue isolated from injured carotid vessels by laser capture microdissection. These data indicate that phenotypic plasticity of smooth muscle cells is highly important to the progression of lumen loss following acute carotid injury. Interference with SEM cell formation could be an innovative approach to combat development of restenosis.

Nox4 promotes endothelial differentiation through chromatin remodeling

RATIONALE

Nox4 is a constitutively active NADPH oxidase that constantly produces low levels of H2O2. Thereby, Nox4 contributes to cell homeostasis and long-term processes, such as differentiation. The high expression of Nox4 seen in endothelial cells contrasts with the low abundance of Nox4 in stem cells, which are accordingly characterized by low levels of H2O2. We hypothesize that Nox4 is a major contributor to endothelial differentiation, is induced during the process of differentiation, and facilitates homeostasis of the resulting endothelial cells.

OBJECTIVE

To determine the role of No×4 in differentiation of murine inducible pluripotent stem cells (miPSC) into endothelial cells (ECs).

METHODS AND RESULTS

miPSC, generated from mouse embryonic wildtype (WT) and Nox4-/- fibroblasts, were differentiated into endothelial cells (miPSC-EC) by stimulation with BMP4 and VEGF. During this process, Nox4 expression increased and knockout of Nox4 prolonged the abundance of pluripotency markers, while expression of endothelial markers was delayed in differentiating Nox4-depleted iPSCs. Eventually, angiogenic capacity of iPSC-ECs is reduced in Nox4 deficient cells, indicating that an absence of Nox4 diminishes stability of the reached phenotype. As an underlying mechanism, we identified JmjD3 as a redox target of Nox4. iPSC-ECs lacking Nox4 display a lower nuclear abundance of the histone demethylase JmjD3, resulting in an increased triple methylation of histone 3 (H3K27me3), which serves as a repressive mark for several genes involved in differentiation.

CONCLUSIONS

Nox4 promotes differentiation of miPSCs into ECs by oxidation of JmjD3 and subsequent demethylation of H3K27me3, which forced endothelial differentiation and stability.

Chronic ischemic heart failure in humans is associated with changes in expression of antigen processing HLA types and activation of T-cells

Background

Sustained pathological inflammation is a hallmark of chronic ischemic heart failure (HF). The short term response to myocardial ischemia has found a protective phenotype for T regulatory cells, yet the extent and consequence of prolonged T-cell activation in chronic ischemic heart failure is unclear.

Methods and results

Single cell RNA sequencing of circulating immune cells (n=181,712 cells) from healthy (n=8) and heart failure donors (n=8) revealed a relative increase in the proportion of activated T cells in heart failure patients relative to healthy controls. T cell activation molecules of the HLA-DR series genes on antigen presenting cells were found to be strongly associated with heart failure patients in the sequencing data, with decreases in antigen processing genes (HLA-DM series) in heart failure patients. Validation via flow cytometry in 27 healthy controls and 43 heart failure patients showed relative decreases of greater than 30% for HLA-DM to HLA-DRB molecule ratios in HF patients (p=0.0082), suggesting an aberrant antigen presentation to T cells linked to autoimmunity in heart failure patients. Additionally, costimulatory molecules such as ICAM-1 (p=0.004) and activation markers like TREM-1 (p=0.04) were elevated in circulating monocytes cells, which may potentiate T cell activation. Correspondingly, a significant and striking decrease in CD4+ and CD8+ naïve T cells along with increases in combined effector memory and TEMRA cells could be evidenced in heart failure patients. Levels of the T-cell homing marker CCR5 were elevated in patients with heart failure. To gain additional insights into potential functional consequences in the heart, supernatants from 3h LPS stimulated immune cells (peripheral blood mononuclear cells or T cells) were applied to various vascular cell types (endothelial cells, pericytes) and with cardiac organoids for 48h. Apoptosis was increased more than 3 fold following incubation with media derived from peripheral blood cells of HF patients, suggesting that immune cells from heart failure patients can directly and indirectly impair cardiovascular cells.

Conclusion

Heart failure is marked by sustained increases in relative proportions of effector T cell and TEMRA populations and homing markers suggesting these cells may undergo extravasation to tissues and deteriorate inflamed myocardium - hastening heart failure progression, worsening prognosis. Further research is required to assess how these cells may migrate to myocardial tissues and what interventions could be useful for blocking myocardial damage.

Funding Acknowledgement

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): DZHK, DGK, SFB

The hydrogen-peroxide producing NADPH oxidase 4 does not limit neointima development after vascular injury in mice

Objective

The NADPH oxidase Nox4 is an important source of H₂O₂. Nox4-derived H₂O₂ limits vascular inflammation and promotes smooth muscle differentiation. On this basis, the role of Nox4 for restenosis development was determined in the mouse carotid artery injury model.

Methods and results

Genetic deletion of Nox4 by a tamoxifen-activated Cre-Lox-system did not impact on neointima formation in the carotid artery wire injury model. To understand this unexpected finding, time-resolved single-cell RNA-sequencing (scRNAseq) from injured carotid arteries of control mice and massive-analysis-of-cDNA-ends (MACE)-RNAseq from the neointima harvested by laser capture microdissection of control and Nox4 knockout mice was performed. This revealed that resting smooth muscle cells (SMCs) and fibroblasts exhibit high Nox4 expression, but that the proliferating de-differentiated SMCs, which give rise to the neointima, have low Nox4 expression. In line with this, the first weeks after injury, gene expression was unchanged between the carotid artery neointimas of control and Nox4 knockout mice.

Conclusion

Upon vascular injury, Nox4 expression is transiently lost in the cells which comprise the neointima. NADPH oxidase 4 therefore does not interfere with restenosis development after wire-induced vascular injury.

Single nuclei sequencing reveals novel insights into cardiac cell signatures in human pediatric dilated cardiopathy

 

The mechanism underlying dilated cardiomyopathy (DCM) in children without a known genetic disorder are unclear. In contrast to adult DCM patients, there is an unmet need for therapeutic options that improve survival in pediatric DCM. Therefore, we performed single nuclei RNA sequencing (snRNA-seq) from heart tissue obtained from children undergoing heart transplantation due to severe heart failure.

We processed heart tissue from 6 children with DCM (EF: 18.67±2.11%) of an age of 0.5, 0.75, 5, 6, 12 and 13 years (y). After snRNA-seq, unsupervised clustering was performed identifying 8 major cell types, including cardiomyocytes (CM), fibroblasts (FB), endothelial cells, leukocytes, pericytes, smooth muscle cells, neuronal-like cells and an endothelial-fibroblast-like cluster. Relative numbers of FB clusters correlated with increasing age of the children which was clinically validated by measuring late enhancement (LE) with cardiac magnetic resonance imaging in 68 pediatric DCM patients. The mean age of patients with LE was 5.86±0.53y vs. 2.36±0.53y in patients without LE (p&lt;0.05). Further analysis of unique highly expressed genes (DEGs) between the 3 age groups identified a profound alteration of gene expression in FB clusters. FBs of explants of &lt;1y old patients showed high expression of anti-fibrotic, development and remodeling associated genes. In contrast, FBs of 12–13y old children highly expressed pro-fibrotic and FB activation associated genes as transforming growth factor beta binding protein (6.63 fold), cytochrome P450 1B1 (3.79 fold), and periostin (7.67 fold) (all p&lt;0.05). Moreover, we observed a switch in collagen expression patterns and in thrombospondin isoforms (from THBS1 to THBS4). Furthermore, our analysis revealed most profound transcriptional changes in CMs. We identified a cluster of CMs with a pro-regenerative profile in &lt;1y old patients, which could not be detected during adolescence. This CM cluster showed high expression of genes associated with proliferation (e.g. cyclin D2), glycolytic metabolism and anti-oxidant markers. Increased cyclin D2 was confirmed by immunostaining (1.43 fold higher in &lt;1y vs. 12–13y). Since all of these gene expression patterns might be affected by the underlying disease of the pediatric heart recipients, we explored their expression in FBs and CMs of postnatal vs. adult mice. Importantly, we could recapitulate the vast majority of the findings from humans in the mice experiments.

Together, these data demonstrate an age-dependent decrease in CM numbers concomitant with increased FBs in pediatric DCM. FBs of &lt;1y old pediatric patients revealed a distinct collagen expression profile and showed lower levels of pro-fibrotic genes. CMs of &lt;1y old donors where characterized with a regeneration enabling gene expression profile, which include pro-proliferative genes. The expression patterns of the CMs indicates, that regeneration might also occur in humans during the firs year of life.

Funding Acknowledgement

Type of funding source: Public grant(s) – EU funding. Main funding source(s): Dr. Rolf M. Schwiete Stiftung, DZHK

DNMT3A clonal hematopoiesis-driver mutations are associated with profound changes in monocyte and T cell signatures in humans with heart failure

Background

Clonal hematopoiesis (CH) driven by mutations of DNA methyltransferase 3a (DNMT3A) is associated with increased incidence of cardiovascular disease and poor prognosis of patients with chronic heart failure (HF) and aortic stenosis. Although experimental studies suggest that DNMT3A CH-driver mutations may enhance inflammation, specific signatures of inflammatory cells in humans are missing. Single-cell RNA-sequencing provides a novel opportunity to define subsets of immune cells mediating inflammation in humans.

Methods

Transcriptomic profiles of peripheral blood mononuclear cells were analysed in N=6 HF patients harboring DNMT3A CH-drived mutations and with HF and N=5 patients with HF and DNMT3A mutations by single-cell RNA-sequencing.

Results

Monocytes of HF patients carrying DNMT3A mutations demonstrated a significantly increased expression of inflammatory genes compared to monocytes derived from patients with HF without DNMT3A mutations. Among the specific up-regulated genes were the prototypic inflammatory interleukins (IL) IL1B, IL6, and IL8, the macrophage inflammatory proteins CCL3 and CCL4 as well as restin, which augments monocyte-endothelial adhesion. The classical monocyte subset of DNMT3A mutation carriers showed increased expression of immunoglobulin superfamily members CD80, CD300LB, and SIGLEC12, as well as the cell adhesion molecule CD58, all of which may be involved in monocyte-T cell interactions. DNMT3A mutation carriers were further characterized by increased expression of T cell receptor chains and Th1, Th17, CD8+ and Treg specific signatures.

Conclusions

This study demonstrates that circulating monocytes and T cells of HF patients harboring CHIP-driver mutations in DNMT3A exhibit a highly inflamed transcriptome, which may contribute to the aggravation of chronic heart failure.

Funding Acknowledgement

Type of funding source: Public Institution(s). Main funding source(s): The German Research Foundation (SFB834, Project B1), and the German Center for Cardiovascular Research (DZHK).

1437Single cell RNA sequencing reveals profound changes in monocytic cell clusters in patients with mutations associated with clonal hematopoiesis

Background

Monocytes and macrophages have distinct roles in cardiovascular health where they may contribute to beneficial processes like wound healing and cardiac conductance or to pathological processes like inflammation, remodeling and fibrosis. Despite their importance, the specific signatures of circulating monocytes are missing. Single cell RNA sequencing (scRNA-seq) provides a novel opportunity to define subsets of monocytes mediating inflammation in humans.

Purpose

To detect and study the inflammatory burden driven by subsets of monocytes in healthy individuals and subjects with chronic ischemic heart failure (CHF) using scRNA-seq.

Methods and results

Circulating CD31+ cells of CHF patients (n=11) along with aged matched (n=3) and young healthy controls (n=5) were sorted and scRNA-seq then performed. Unsupervised clustering of present sequencing data revealed these cells to be comprised of 19 subpopulations (primarily monocytes). Many subpopulations of cells were comprised chiefly or solely by CHF subjects. Dysregulated genes in CHF subjects, relative to healthy controls included interleukin-1b, thrombospondin-1, S100A8 and matrix metalloprotease-1, which were confirmed by FACS and qRT-PCR in a validation cohort. Given the expanded, divergent and highly inflammatory transcriptional populations of monocytes in patients with CHF, we assessed whether occurrence of somatic mutations associated with clonal hematopoiesis of indeterminate potential (CHIP), recently shown to be increased in subjects with atherosclerosis and heart failure, might occur in these subjects. Indeed, we identified patients who revealed mutations in the DNA methyltransferase DNMT3A and other CHIP-driver genes. DNMT3A mutations were associated with changes in known DNMT3A target genes such as the pro-inflammatory genes CXCL1, CXCL2 and IL6 in circulating monocytic cells. Moreover, cell fate trajectory analysis showed shared fates of cells driven by pseudotime-dependent variables from subjects harboring DNMT3A mutations. Regulated genes in this fate were associated with cell survival, migration and inflammation, appropriate for this disease phenotype.

Conclusions

This is the first study to show scRNA-seq profiles of monocytes in patients with CHF. Healthy subjects displayed remarkable homogeneity in their transcriptional profiles. CHF subjects show changes in inflammatory gene expression. CHF subjects with clonal hematopoiesis share signature gene expression profiles driving similar cell fates. Subjects with CHF of ischemic origin harboring DNMT3A mutations have a worse prognosis than non-CHIP carrier CHF controls. Identification of early alterations in immune cell subsets recognized by single cell sequencing and genetic testing of CHIP mutations may detect subjects with a high risk and allow for a precision treatment of the immune disorders.

Acknowledgement/Funding

SFB834

6091Chronic heart failure is associated with inflammatory deterioration of the bone marrow vascular niche

Introduction

Inflammation plays a crucial role in many aspects of cardiovascular disease. Particularly, acquired mutations of hematopoietic stem cells (HSC) leading to clonal expansion of inflammatory cells (CHIP) are increased with age and are associated with an enhanced risk of cardiovascular disease. The bone marrow (BM) vascular niche plays a crucial role in maintenance and regulation of HSC functions. Previous studies in mice showed the reduction of a specific Endomucin-high (H-type) endothelial cells (EC) subpopulation by aging. However, the impact of cardiovascular disease is unclear. Therefore, we aimed to investigate the effects of age and heart failure (HF) on the vascular BM cell composition in mice and humans.

Methods and results

Aging mice showed an age-dependent decrease of type H (Emcn-high) BM ECs (p=0.004), whereas the BM frequencies of type L (Emcn-low) ECs did not significantly differ (P=0.18). Importantly, we also observed a marked reduction of type H EC in chronic ischemic mice (P=0.016 vs. sham) indicating that chronic ischemic HF induces similar alterations of the vascular stem cell niche. Importantly, type H ECs were also significantly reduced in ischemic HF patients (n=16) compared with control subjects (n=8; P=0.0003). To gain insights into the mechanisms underlying the changes in the vascular niche, we performed single cells RNA sequencing of human BM ECs. These studies confirmed the decrease in Emcn-expressing ECs in ischemic HF patients, which was accompanied by significantly increased expression of inflammatory genes, including IL1b (P<0.0001 vs. control). Inflammatory EC phenotypes and IL1b expression in HF could be further confirmed at protein level using cytospin immunostainings. Finally, we comprehensively evaluated phenotype-associated differences in the bone marrow plasma proteomes of healthy individuals (n=19) and patients with chronic ischemic (n=22) and non-ischemic (n=19) HF, using proximity extension assays. Here, we identified 182 proteins significantly differentially regulated in CHF versus CTRL. Among the top upregulated proteins the BM environment of patients with CHF showed a striking enrichment of inflammatory and ECM remodeling components.

Conclusions

Our data show for the first time an impact of chronic heart failure on the bone marrow vascular niche in humans. These changes seem to be strongly associated with increased inflammatory response and bone matrix remodeling in CHF. Specifically, the induction of the inflammatory cytokine IL1b may contribute to the disturbed phenotype suggesting that inhibition of IL1b (e.g. by canakinumab) may be used as a novel strategy to prevent or reverse the deterioration of the vascular BM niche.

Carnosine Supplementation Mitigates the Deleterious Effects of Particulate Matter Exposure in Mice

Background Exposure to fine airborne particulate matter ( PM _2.5) induces quantitative and qualitative defects in bone marrow-derived endothelial progenitor cells of mice, and similar outcomes in humans may contribute to vascular dysfunction and the cardiovascular morbidity and mortality associated with PM _2.5 exposure. Nevertheless, mechanisms underlying the pervasive effects of PM _2.5 are unclear and effective interventional strategies to mitigate against PM _2.5 toxicity are lacking. Furthermore, whether PM _2.5 exposure affects other types of bone marrow stem cells leading to additional hematological or immunological dysfunction is not clear. Methods and Results Mice given normal drinking water or that supplemented with carnosine, a naturally occurring, nucleophilic di-peptide that binds reactive aldehydes, were exposed to filtered air or concentrated ambient particles. Mice drinking normal water and exposed to concentrated ambient particles demonstrated a depletion of bone marrow hematopoietic stem cells but no change in mesenchymal stem cells. However, HSC depletion was significantly attenuated when the mice were placed on drinking water containing carnosine. Carnosine supplementation also increased the levels of carnosine-propanal conjugates in the urine of CAPs-exposed mice and prevented the concentrated ambient particles-induced dysfunction of endothelial progenitor cells as assessed by in vitro and in vivo assays. Conclusions These results suggest that exposure to PM _2.5 has pervasive effects on different bone marrow stem cell populations and that PM _2.5-induced hematopoietic stem cells depletion, endothelial progenitor cell dysfunction, and defects in vascular repair can be mitigated by excess carnosine. Carnosine supplementation may be a viable approach for preventing PM _2.5-induced immune dysfunction and cardiovascular injury in humans.

Benzene exposure is associated with cardiovascular disease risk

Benzene is a ubiquitous, volatile pollutant present at high concentrations in toxins (e.g. tobacco smoke) known to increase cardiovascular disease (CVD) risk. Despite its prevalence, the cardiovascular effects of benzene have rarely been studied. Hence, we examined whether exposure to benzene is associated with increased CVD risk. The effects of benzene exposure in mice were assessed by direct inhalation, while the effects of benzene exposure in humans was assessed in 210 individuals with mild to high CVD risk by measuring urinary levels of the benzene metabolite trans,trans-muconic acid (t,t-MA). Generalized linear models were used to assess the association between benzene exposure and CVD risk. Mice inhaling volatile benzene had significantly reduced levels of circulating angiogenic cells (Flk-1⁺/Sca-1⁺) as well as an increased levels of plasma low-density lipoprotein (LDL) compared with control mice breathing filtered air. In the human cohort, urinary levels of t,t-MA were inversely associated several populations of circulating angiogenic cells (CD31⁺/34⁺/45⁺, CD31⁺/34⁺/45⁺/AC133^–, CD34⁺/45⁺/AC133⁺). Although t,t-MA was not associated with plasma markers of inflammation or thrombosis, t,t-MA levels were higher in smokers and in individuals with dyslipidemia. In smokers, t,t-MA levels were positively associated with urinary metabolites of nicotine (cotinine) and acrolein (3-hydroxymercapturic acid). Levels of t,t-MA were also associated with CVD risk as assessed using the Framingham Risk Score and this association was independent of smoking. Thus, benzene exposure is associated with increased CVD risk and deficits in circulating angiogenic cells in both smokers and non-smokers.

Exposure to Fine Particulate Air Pollution Is Associated With Endothelial Injury and Systemic Inflammation

RATIONALE

Epidemiological evidence indicates that exposures to fine particulate matter air pollution (PM_2.5) contribute to global burden of disease, primarily as a result of increased risk of cardiovascular morbidity and mortality. However, mechanisms by which PM_2.5 exposure induces cardiovascular injury remain unclear. PM_2.5-induced endothelial dysfunction and systemic inflammation have been implicated, but direct evidence is lacking.

OBJECTIVE

To examine whether acute exposure to PM_2.5 is associated with endothelial injury and systemic inflammation.

METHODS AND RESULTS

Blood was collected from healthy, nonsmoking, young adults during 3 study periods that included episodes of elevated PM_2.5 levels. Microparticles and immune cells in blood were measured by flow cytometry, and plasma cytokine/growth factors were measured using multiplexing laser beads. PM_2.5 exposure was associated with the elevated levels of endothelial microparticles (annexin V⁺/CD41^-/CD31⁺), including subtypes expressing arterial-, venous-, and lung-specific markers, but not microparticles expressing CD62⁺. These changes were accompanied by suppressed circulating levels of proangiogenic growth factors (EGF [epidermal growth factor], sCD40L [soluble CD40 ligand], PDGF [platelet-derived growth factor], RANTES [regulated on activation, normal T-cell-expressed and secreted], GROα [growth-regulated protein α], and VEGF [vascular endothelial growth factor]), and an increase in the levels of antiangiogenic (TNFα [tumor necrosis factor α], IP-10 [interferon γ-induced protein 10]), and proinflammatory cytokines (MCP-1 [monocyte chemoattractant protein 1], MIP-1α/β [macrophage inflammatory protein 1α/β], IL-6 [interleukin 6], and IL-1β [interleukin 1β]), and markers of endothelial adhesion (sICAM-1 [soluble intercellular adhesion molecule 1] and sVCAM-1 [soluble vascular cellular adhesion molecule 1]). PM_2.5 exposure was also associated with an inflammatory response characterized by elevated levels of circulating CD14⁺, CD16⁺, CD4⁺, and CD8⁺, but not CD19⁺ cells.

CONCLUSIONS

Episodic PM_2.5 exposures are associated with increased endothelial cell apoptosis, an antiangiogenic plasma profile, and elevated levels of circulating monocytes and T, but not B, lymphocytes. These changes could contribute to the pathogenic sequelae of atherogenesis and acute coronary events.

Abstract 132: Biomarkers of Cardiovascular Toxicity Following Benzene Exposure

Benzene is a ubiquitous environmental pollutant abundant in plastics, petroleum products and cigarette smoke. Although hematopoietic and hepatic toxicity of benzene has been extensively studied, little is known about the effect of benzene on cardiovascular health. In this study, we assessed benzene exposure in a cohort of 210 participants with moderate to high CVD risk by measuring urinary benzene metabolite - trans, trans-muconic acid (t,t-MA). After adjusting for confounding variables we observed a 9% decrease in circulating levels of both early (AC133+) and late (AC133-) angiogenic cells for every 0.1mg t,t-MA/g creatinine increase in the urine. Uriniary t,t,MA levels were also positively associated with hyperlipidemia (P<0.02). Although smoking was associated with higher urinary levels of, t,t-MA, the association between benzene exposure and CVD risk was independent of smoking. In non-smokers, t,t-MA levels were positively associated with increased Framingham Risk Scores. Next, we examined the association of surrogate markers of cardiovascular functions and injury in male C57BL/6 mice exposed to HEPA-filtered air or benzene (50 ppm) for 6 hours/day for two (n=34/treatment) or six weeks (n=20/treatment). Both at two and six weeks of exposure to benzene increased fasting plasma glucose (13%, P<0.05), fasting insulin (39%, P<0.05) and HOMA-IR (72%, P<0.05); and platelet-leukocyte aggregates (PLAggs), a marker of platelet activation in vivo. This was accompanied by 26% decrease (P<0.05) in hepatic reduced glutathione level and activation of NF-κB in the liver and skeletal muscle. Moreover, after 6 weeks of benzene exposure plasma LDL and HDL were increased by 25% (P<0.05) and 5% (P<0.05) respectively; circulating endothelial microparticles were increased by 60% (P<0.05); and blood endothelial progenitor cells (EPCs) were decreased by 52% (P<0.05). These data suggest that exposure to benzene is associated with potential deficits in vascular repair and increased CVD risk.

Acrolein decreases endothelial cell migration and insulin sensitivity through induction of let-7a

Acrolein is a major reactive component of vehicle exhaust, and cigarette and wood smoke. It is also present in several food substances and is generated endogenously during inflammation and lipid peroxidation. Although previous studies have shown that dietary or inhalation exposure to acrolein results in endothelial activation, platelet activation, and accelerated atherogenesis, the basis for these effects is unknown. Moreover, the effects of acrolein on microRNA (miRNA) have not been studied. Using AGILENT miRNA microarray high-throughput technology, we found that treatment of cultured human umbilical vein endothelial cells with acrolein led to a significant (>1.5-fold) upregulation of 12, and downregulation of 15, miRNAs. Among the miRNAs upregulated were members of the let-7 family and this upregulation was associated with decreased expression of their protein targets, β3 integrin, Cdc34, and K-Ras. Exposure to acrolein attenuated β3 integrin-dependent migration and reduced Akt phosphorylation in response to insulin. These effects of acrolein on endothelial cell migration and insulin signaling were reversed by expression of a let-7a inhibitor. Also, inhalation exposure of mice to acrolein (1 ppm x 6 h/day x 4 days) upregulated let-7a and led to a decrease in insulin-stimulated Akt phosphorylation in the aorta. These results suggest that acrolein exposure has broad effects on endothelial miRNA repertoire and that attenuation of endothelial cell migration and insulin signaling by acrolein is mediated in part by the upregulation of let-7a. This mechanism may be a significant feature of vascular injury caused by inflammation, oxidized lipids, and exposure to environmental pollutants.

Ergosterol (major sterol of baker's and brewer's yeast extracts) inhibits the growth of human breast cancer cells in vitro and the potential role of its oxidation products

The derivation of chemopreventive agents from dietary sources has been the subject of considerable attention in recent years. Yeast extracts have been used as nutritional supplements for a number of years. In this communication we show that ergosterol (a 28-carbon sterol found in baker's and brewer's yeast) can prevent growth of breast cancer cells in vitro in the presence of estradiol-17 beta. Estrogen receptor (+) MCF-7 cells appear to be more sensitive to ergosterol than estrogen receptor (-) MDA-231 cells. However, MDA-231 cells were more sensitive to ergosterol in terms of apoptotic effects than MCF-7 cells, indicating that other mechanisms (antiestrogenic activity) may also be operative in estrogen receptor (+) cells. Compared to freshly prepared ergosterol, stored preparations were more potent in inhibiting growth of cancer cells, indicating that oxidation product(s) of ergosterol may be responsible for the noted effects. Further studies on in vivo effects of ergosterol and lipid extracts of yeast in animal models are warranted to determine their potential for use as supplements in humans.

Uptake and protection against oxidative stress by estrogen esters in THP-1 human macrophage cell lines

Estrogen replacement therapy offers protection from coronary artery disease in postmenopausal women. However, there is serious concern that long-term unopposed estrogen use increases the risk of breast and endometrial cancer through estrogen-receptor-driven mechanisms. In this communication, we have explored an alternate route of estrogen delivery to macrophages using hydrophobic derivatives that associate with lipoproteins. Unlike free estradiol (E(2)), long-chain fatty acid esters of E(2) associate extensively with low-density lipoprotein (LDL). In THP-1 cells, E(2) esters accumulated to a significantly higher level when compared to E(2) in the presence of LDL. In the presence of oxidized LDL even greater amounts of E(2) esters accumulated in cells. In THP-1 cells, E(2) esters were capable of preventing the azo-bis-induced increase in oxidative stress (hydrogen peroxide formation). These studies suggest that (a) hydrophobic esters of estrogens that associate with LDL can be delivered to macrophages and (b) these esters can effectively function as antioxidants protecting against oxidative stress.

Evidence for the role of high density lipoproteins in mediating the antioxidant effect of estrogens

Estrogens possess strong antioxidant effects in vitro, but in vivo studies in humans have yielded conflicting results. Little is known regarding factors that mediate the antioxidant effect of estrogens in vivo. In this study the potential role of high density lipoprotein (HDL) was examined. The antioxidant effect of estradiol-17beta (E2) added to low density lipoprotein (LDL) was lost after dialysis. In contrast, the antioxidant effect of E2 added to HDL was conserved after dialysis, suggesting that E2 was bound to HDL. Binding of E2 to LDL increased after esterification (especially to long chain fatty acids). In the presence of HDL, an increased amount of E2 was transferred to LDL. E2-17 ester was as potent as E2 in preventing LDL oxidation in vitro, but 3,17-diesters were not as effective (E2=E2-17 ester>E2-3 ester>E2-3,17 diester). This was also supported by experiments which showed that estrogens with masked 3-OH groups were not effective as antioxidants. These studies provide evidence that HDL could facilitate the antioxidant effect of E2 through initial association, esterification and eventual transfer of E2 esters to LDL. Therefore it is critical that HDL peroxidation parameters be evaluated in subjects receiving estrogen replacement therapy.

Evidence for interference in estradiol-17beta inactivation to estrone by oxidized low-density lipoprotein and selected lipid peroxidation products

An elevation in plasma estrogen levels is believed to play a key role in the pathogenesis of breast cancer. The conversion of estradiol-17beta (E2) to estrone (E1) by 17beta-hydroxy steroid dehydrogenase type 4 (17-HSD4) represents a major pathway of its inactivation in cells. In this study the potential relationship between lipoprotein peroxidation products and E2 metabolism was examined. It was noted that oxidized low-density lipoprotein (OX-LDL), not native LDL, caused a time- and concentration-dependent inhibition of the conversion of labeled E2 to E1 in THP-1 macrophage cells. Further studies noted that among the lipoprotein peroxidation products examined, malondialdehyde (MDA) caused a marked decrease in this reaction, whereas hexanal and a variety of oxysterols had no effect. This inhibition of E1 formation from E2 in THP-1 cells was confirmed by the quantitation of estrone formed with high-pressure liquid chromatography and by the expression of 17-HSD4 by reverse transcriptase-polymerase chain reaction. MDA added to Hep G2 cells showed a similar trend in E1 formation. These results suggest that increased oxidative stress and lipid peroxidation might result in decreased inactivation of biologically active estrogen. This might be important in postmenopausal women undergoing estrogen replacement therapy.

Mechanisms involved in the protective effect of estradiol-17beta on lipid peroxidation and DNA damage

Previous studies from our laboratory have shown that estrogens can protect against lipoprotein peroxidation and DNA damage. In this study, the mechanism of estradiol-17beta (E2) action was investigated by comparing E2 with selective scavengers of reactive oxygen species (ROS) in terms of inhibition of 1) human low-density lipoprotein (LDL) peroxidation (measured by the diene conjugation method) and 2) DNA damage (measured by the formation of strand breaks in supercoiled OX-174 RFI DNA). In addition, the direct effect of E2 on the generation of individual ROS was also measured. By use of ROS scavengers, it was determined that lipoprotein peroxidation was predominantly due to superoxide (39%), with some contributions from hydrogen peroxide (23%) and peroxy (38%) radicals. E2 was a more effective inhibitor of peroxidation than all the ROS scavengers combined. In DNA damage, scavengers of hydrogen peroxide, hydroxyl, and superoxide radical offered significant protection (49-65%). E2 alone offered a similar degree of protection, and no additional effect was evident when it was combined with ROS scavengers. E2 caused a significant reduction (37%) in the production of superoxide radical by bovine heart endothelial cells in culture but had no effect on the formation of either hydrogen peroxide or hydroxyl radicals. These studies show that 1) the protection offered by E2 in terms of lipid peroxidation could be due to its ability to inhibit generation of superoxide radical and prevent further chain propagation, and 2) in DNA damage protection, E2 mainly appears to inhibit chain propagation.

Association of estrogens with human plasma lipoproteins: studies using estradiol-17beta and its hydrophobic derivative

Estrogen replacement therapy is widely used to combat symptoms of menopause, but factors influencing the transport of estrogen in plasma and its cellular uptake have been explored only to a limited extent. In this study, labeled estradiol-17beta (E2) was compared with its hydrophobic derivative (estradiol-3,17-diacetate, E2AA) in terms of (1) distribution within various lipoproteins and lipoprotein-free fractions of human plasma by ultracentrifugation and (2) uptake by human endothelial cells. Although added E2 was predominantly bound to HDL and lipoprotein-free fractions, E2AA was associated to some degree with VLDL and LDL but was still present in significant amounts in HDL and lipoprotein-free fractions. Significant associations of E2 with lipoproteins were also confirmed by polyacrylamide gel electrophoretic separation of E2-labeled plasma. In normal plasma, however, <10% of E2 was associated with lipoproteins when measured by radioimmunoassay. Incubation of E2AA and E2 with human dermal capillary endothelial cells showed similar uptake by 24 hours. A significant portion of E2AA was hydrolyzed to estradiol-17-monoacetate both in plasma and in cells. The addition of HDL and LDL to medium containing lipoprotein-deficient serum significantly reduced labeled E2 and E2AA uptake, respectively, by endothelial cells. These studies suggest that (1) although the association of E2 with HDL under normal conditions may be small, it increases significantly with higher estrogen concentrations of E2; (2) the hydrophobic ester of E2 shows increased binding to VLDL and LDL; and (3) this approach may be useful in manipulating the delivery of selected E2 derivatives to cells.

Superior and distinct antioxidant effects of selected estrogen metabolites on lipid peroxidation

The effect of the estrogen metabolites, 4-hydroxyestrone and 17alpha-dihydroequilin (metabolites of estradiol-17beta and equilin, respectively), were examined for antioxidant effects on plasma and lipoprotein lipid peroxidation . Lipid peroxidation was evaluated by products of both fatty acid (thiobarbituric acid-reactive substances [TBARS]) and cholesterol (oxysterols) oxidation from lipoproteins or whole plasma. Although all estrogens significantly reduced lipid peroxidation, 4-hydroxyestrone was far more potent than either equilin or 17alpha-dihydroequilin in inhibiting TBARS formation in lipoproteins induced by Cu2+. Similar effects were also noted on TBARS formation in THP-l macrophages in culture. However, 17alpha-dihydroequilin (along with equilin) strongly inhibited oxysterol formation, whereas 4-hydroxyestrone was ineffective. These studies suggest that different estrogens might act preferentially on distinct lipid substrates in exhibiting antioxidant effects.

Antioxidant potential of specific estrogens on lipid peroxidation

Coronary heart disease (CHD) is the leading cause of death in postmenopause. Estrogen administration in postmenopause lowers the risk of CHD by 50%. A variety of estrogen preparations are currently used in postmenopausal hormone replacement therapy. It is unknown, however, if structural differences in the estrogen molecule influence the cardioprotective effects of estrogens. In this communication we have shown that equine estrogens (especially equilin) exhibit higher antioxidant potency (as measured by fatty acids and sterols oxidation) when compared to estrone and estradiol-17 beta.