Infectious agents are not necessary for murine atherogenesis

Evidence further linking the intestine to cardiovascular disease

PURPOSE OF REVIEW

To review recent publications linking the intestine to cardiovascular disease.

RECENT FINDINGS

Aromatic amino acid-derived metabolites produced by gut-bacteria were identified that increased or decreased the risk of cardiovascular events. Dietary phenylalanine was metabolized to phenylacetic acid by gut microbes, and converted into phenylacetylglutamine by the host, which increased thrombosis potential via adrenergic receptors and was associated with increased major adverse cardiovascular events. Another microbiota-associated metabolite of aromatic amino acids, indole-3-propionic acid, protected against heart failure with preserved ejection fraction. The mechanism by which dietary cholesterol is absorbed was found to involve the Nieman-Pick C1-like1 protein working together with a newly discovered protein called Aster. Levels of gut-derived bacterial lipopolysaccharide in serum that are an order of magnitude less than those seen in gram negative sepsis were shown to play a role in enhancing atherosclerosis and thrombosis.

SUMMARY

Promising new therapeutic targets in the intestine for preventing or treating cardiovascular disease have been identified.

Gut Microbiota and Microbial Metabolism in Early Risk of Cardiometabolic Disease

Cardiometabolic disease comprises cardiovascular and metabolic dysfunction and underlies the leading causes of morbidity and mortality, both within the United States and worldwide. Commensal microbiota are implicated in the development of cardiometabolic disease. Evidence suggests that the microbiome is relatively variable during infancy and early childhood, becoming more fixed in later childhood and adulthood. Effects of microbiota, both during early development, and in later life, may induce changes in host metabolism that modulate risk mechanisms and predispose toward the development of cardiometabolic disease. In this review, we summarize the factors that influence gut microbiome composition and function during early life and explore how changes in microbiota and microbial metabolism influence host metabolism and cardiometabolic risk throughout life. We highlight limitations in current methodology and approaches and outline state-of-the-art advances, which are improving research and building toward refined diagnosis and treatment options in microbiome-targeted therapies.

Antibiotic-induced gut microbiota depletion exacerbates host hypercholesterolemia

Hypercholesterolemia is a major driver of atherosclerosis, thus contributing to high morbidity and mortality worldwide. Gut microbiota have been identified as modulator of blood lipids including cholesterol levels. Few studies have already linked certain bacteria and microbial mechanisms to host cholesterol. However, in particular mouse models revealed conflicting results depending on genetics and experimental protocol. To gain further insights into the relationship between intestinal bacteria and host cholesterol metabolism, we first performed fecal 16S rRNA targeted metagenomic sequencing in a human cohort (n = 24) naïve for cholesterol lowering drugs. Here, we show alterations in the gut microbiota composition of hypercholesterolemic patients with depletion of Bifidobacteria, expansion of Clostridia and increased Firmicutes/Bacteroidetes ratio. To test whether pharmacological intervention in gut microbiota impacts host serum levels of cholesterol, we treated hypercholesterolemic Apolipoprotein E knockout with oral largely non-absorbable antibiotics. Antibiotics increased serum cholesterol, but only when mice were fed normal chow diet and cholesterol was measured in the random fed state. These elevations in cholesterol already occurred few days after treatment initiation and were reversible after stopping antibiotics with re-acquisition of intestinal bacteria. Gene expression analyses pointed to increased intestinal cholesterol uptake mediated by antibiotics in the fed state. Non-targeted serum metabolomics suggested that diminished plant sterol levels and reduced bile acid cycling were involved microbial mechanisms. In conclusion, our work further enlightens the link between gut microbiota and host cholesterol metabolism. Pharmacological disruption of the gut flora by antibiotics was able to exacerbate serum cholesterol and may impact cardiovascular disease.

The IL-1 Family and Its Role in Atherosclerosis

The IL-1 superfamily of cytokines is a central regulator of immunity and inflammation. The family is composed of 11 cytokines (with agonist, antagonist, and anti-inflammatory properties) and 10 receptors, all tightly regulated through decoy receptor, receptor antagonists, and signaling inhibitors. Inflammation not only is an important physiological response against infection and injury but also plays a central role in atherosclerosis development. Several clinical association studies along with experimental studies have implicated the IL-1 superfamily of cytokines and its receptors in the pathogenesis of cardiovascular disease. Here, we summarize the key features of the IL-1 family, its role in immunity and disease, and how it helps shape the development of atherosclerosis.

LDL delivery of microbial small RNAs drives atherosclerosis through macrophage TLR8

Macrophages present a spectrum of phenotypes that mediate both the pathogenesis and resolution of atherosclerotic lesions. Inflammatory macrophage phenotypes are pro-atherogenic, but the stimulatory factors that promote these phenotypes remain incompletely defined. Here we demonstrate that microbial small RNAs (msRNA) are enriched on low-density lipoprotein (LDL) and drive pro-inflammatory macrophage polarization and cytokine secretion via activation of the RNA sensor toll-like receptor 8 (TLR8). Removal of msRNA cargo during LDL re-constitution yields particles that readily promote sterol loading but fail to stimulate inflammatory activation. Competitive antagonism of TLR8 with non-targeting locked nucleic acids was found to prevent native LDL-induced macrophage polarization in vitro, and re-organize lesion macrophage phenotypes in vivo, as determined by single-cell RNA sequencing. Critically, this was associated with reduced disease burden in distinct mouse models of atherosclerosis. These results identify LDL-msRNA as instigators of atherosclerosis-associated inflammation and support alternative functions of LDL beyond cholesterol transport.

Circulating gut microbiota-related metabolites influence endothelium plaque lesion formation in ApoE knockout rats

Atherosclerosis is the main cause of cardiac and peripheral vessel infarction in developed countries. Recent studies have established that gut microbiota and their metabolites play important roles in the development and progression of cardiovascular disease; however, the underlying mechanisms remain unclear. The present study aimed to investigate endothelium plaque lesion formation in ApoE-deficient rats fed a normal chow diet under germ-free (GF) and specific-pathogen-free (SPF) conditions at various time points. There was no difference in serum cholesterol and triglyceride levels between SPF-rats and GF-rats. Histological studies revealed that the GF-rats developed endothelium plaques in the aorta from 26 to 52 weeks, but this was not observed in SPF-rats. GF-rat coronary arteries had moderate-to-severe endothelium lesions during this time period, but SPF-rat coronary arteries had only mild lesion formation. Immunohistochemical staining showed higher accumulation of CD68-positive and arginase-negative foamy-like macrophages on the arterial walls of GF-rats, and expression of TNF-α and IL-6 in foam cells was only observed in GF-rats. In addition, microbial metabolites, including equol derivatives, enterolactone derivatives, indole-3-propionate, indole-3-acrylic acid, cholic acid, hippuric acid, and isoquinolone, were significantly higher in the SPF group than in the GF group. In conclusion, our results indicate that gut microbiota may attenuate atherosclerosis development.

Microbiome and Cardiovascular Disease

Atherosclerotic cardiovascular disease (ASCVD) is a prime example of a systems disease. In the initial phase, apolipoprotein B-containing cholesterol-rich lipoproteins deposit excess cholesterol in macrophage-like cells that subsequently develop into foam cells. A multitude of systemic as well as environmental factors are involved in further progression of atherosclerotic plaque formation. In recent years, both oral and gut microbiota have been proposed to play an important role in the process at different stages. Particularly bacteria from the oral cavity may easily reach the circulation and cause low-grade inflammation, a recognized risk factor for ASCVD. Gut-derived microbiota on the other hand can influence host metabolism on various levels. Next to translocation across the intestinal wall, these prokaryotes produce a great number of specific metabolites such as trimethylamine and short-chain fatty acids but can also metabolize endogenously formed bile acids and convert these into metabolites that may influence signal transduction pathways. In this overview, we critically discuss the novel developments in this rapidly emerging research field.

Network of Interactions Between Gut Microbiome, Host Biomarkers, and Urine Metabolome in Carotid Atherosclerosis

Comprehensive analyses of multi-omics data may provide insights into interactions between different biological layers concerning distinct clinical features. We integrated data on the gut microbiota, blood parameters and urine metabolites of treatment-naive individuals presenting a wide range of metabolic disease phenotypes to delineate clinically meaningful associations. Trans-omics correlation networks revealed that candidate gut microbial biomarkers and urine metabolite feature were covaried with distinct clinical phenotypes. Integration of the gut microbiome, the urine metabolome and the phenome revealed that variations in one of these three systems correlated with changes in the other two. In a specific note about clinical parameters of liver function, we identified Eubacteriumeligens, Faecalibacteriumprausnitzii and Ruminococcuslactaris to be associated with a healthy liver function, whereas Clostridium bolteae, Tyzzerellanexills, Ruminococcusgnavus, Blautiahansenii, and Atopobiumparvulum were associated with blood biomarkers for liver diseases. Variations in these microbiota features paralleled changes in specific urine metabolites. Network modeling yielded two core clusters including one large gut microbe-urine metabolite close-knit cluster and one triangular cluster composed of a gut microbe-blood-urine network, demonstrating close inter-system crosstalk especially between the gut microbiome and the urine metabolome. Distinct clinical phenotypes are manifested in both the gut microbiome and the urine metabolome, and inter-domain connectivity takes the form of high-dimensional networks. Such networks may further our understanding of complex biological systems, and may provide a basis for identifying biomarkers for diseases. Deciphering the complexity of human physiology and disease requires a holistic and trans-omics approach integrating multi-layer data sets, including the gut microbiome and profiles of biological fluids. By studying the gut microbiome on carotid atherosclerosis, we identified microbial features associated with clinical parameters, and we observed that groups of urine metabolites correlated with groups of clinical parameters. Combining the three data sets, we revealed correlations of entities across the three systems, suggesting that physiological changes are reflected in each of the omics. Our findings provided insights into the interactive network between the gut microbiome, blood clinical parameters and the urine metabolome concerning physiological variations, and showed the promise of trans-omics study for biomarker discovery.

Implications for the role of lipopolysaccharide in the development of atherosclerosis

Mounting scientific evidence over decades has established that atherosclerosis is a chronic inflammatory disorder. Among the potentially critical sources of vascular inflammation during atherosclerosis are the components of pathogenic bacteria, especially lipopolysaccharide (LPS). Toll-like receptor (TLR)-4, expressed on different inflammatory cells involved with the recognition of bacterial LPS, has been recognized to have mutations that are prevalent in a number of ethnic groups. Such mutations have been associated with a decreased risk of atherosclerosis. In addition, epidemiological investigations have proposed that LPS confers a risk factor for the development of atherosclerosis. Gram-negative bacteria are the major source of LPS in an individual's serum, which may be generated during subclinical infections. The major cell receptors on inflammatory cells involved in the pathogenesis of atherosclerosis, like macrophages, monocytes, and dendritic cells (DCs), are CD14, MD-2, and LPS binding protein (LBP). These receptors have been blamed for the development of atherosclerosis through dysregulated activation following LPS recognition. Lipoproteins may also play a role in modulating the LPS-induced inflammatory events during atherosclerosis development. In this review article, we attempt to clarify the role of LPS in the initiation and progression of atherosclerotic lesion development.

Atherosclerosis and Inflammatory Bowel Disease-Shared Pathogenesis and Implications for Treatment

Atherosclerosis and inflammatory bowel disease (IBD) are often regarded as 2 distinct entities. The commonest manifestation of atherosclerosis is ischemic heart disease (IHD), and an association between IHD and IBD has been reported. Atherosclerosis and IBD share common pathophysiological mechanisms in terms of their genetics, immunology, and contributing environmental factors. Factors associated with atherosclerosis are implicated in the development of IBD and vice versa. Therefore, treatments targeting the common pathophysiology pathways may be effective in both conditions. The current review considers the pathophysiological pathways that are shared between the 2 conditions and discusses the implications for treatment and research.

Germ-free housing conditions do not affect aortic root and aortic arch lesion size of late atherosclerotic low-density lipoprotein receptor-deficient mice

The microbiota has been linked to the development of atherosclerosis, but the functional impact of these resident bacteria on the lesion size and cellular composition of atherosclerotic plaques in the aorta has never been experimentally addressed with the germ-free low-density lipoprotein receptor-deficient (Ldlr^-/- ) mouse atherosclerosis model. Here, we report that 16 weeks of high-fat diet (HFD) feeding of hypercholesterolemic Ldlr^-/- mice at germ-free (GF) housing conditions did not impact relative aortic root plaque size, macrophage content, and necrotic core area. Likewise, we did not find changes in the relative aortic arch lesion size. However, late atherosclerotic GF Ldlr^-/- mice had altered inflammatory plasma protein markers and reduced smooth muscle cell content in their atherosclerotic root plaques relative to CONV-R Ldlr^-/- mice. Neither absolute nor relative aortic root or aortic arch plaque size correlated with age. Our analyses on GF Ldlr^-/- mice did not reveal a significant contribution of the microbiota in late aortic atherosclerosis.

Mechanisms of NLRP3 priming in inflammaging and age related diseases

The NLRP3 inflammasome is a vital part of the innate immune response, whilst its aberrant activation drives the progression of a number of non-communicable diseases. Thus, NLRP3 inflammasome assembly must be tightly controlled at several checkpoints. The priming step of NLRP3 inflammasome activation is associated with increased NLRP3 gene expression, as well as post-translational modifications that control NLRP3 levels and licence the NLRP3 protein for inflammasome assembly. Increasing life expectancy in modern society is accompanied by a growing percentage of elderly individuals. The process of aging is associated with chronic inflammation that drives and/or worsens a range of age related non-communicable conditions. The NLRP3 inflammasome is known to contribute to pathological inflammation in many settings, but the mechanisms that prime NLRP3 for activation throughout aging and related co-morbidities have not been extensively reviewed. Here we dissect the biochemical changes that occur during aging and the pathogenesis of age related diseases and analyse the mechanisms by which they prime the NLRP3 inflammasome, thus exacerbating inflammation.

Implication of Gut Microbiota in Cardiovascular Diseases

Emerging evidence has identified the association between gut microbiota and various diseases, including cardiovascular diseases (CVDs). Altered intestinal flora composition has been described in detail in CVDs, such as hypertension, atherosclerosis, myocardial infarction, heart failure, and arrhythmia. In contrast, the importance of fermentation metabolites, such as trimethylamine N-oxide (TMAO), short-chain fatty acids (SCFAs), and secondary bile acid (BA), has also been implicated in CVD development, prevention, treatment, and prognosis. The potential mechanisms are conventionally thought to involve immune regulation, host energy metabolism, and oxidative stress. However, numerous types of programmed cell death, including apoptosis, autophagy, pyroptosis, ferroptosis, and clockophagy, also serve as a key link in microbiome-host cross talk. In this review, we introduced and summarized the results from recent studies dealing with the relationship between gut microbiota and cardiac disorders, highlighting the role of programmed cell death. We hope to shed light on microbiota-targeted therapeutic strategies in CVD management.

Mitochondrial Contact Sites in Inflammation-Induced Cardiovascular Disease

The mitochondrion, the ATP-producing center, is both physically and functionally associated with almost all other organelles in the cell. Mitochondrial-associated membranes (MAMs) are involved in a variety of biological processes, such as lipid exchange, protein transport, mitochondrial fission, mitophagy, and inflammation. Several inflammation-related diseases in the cardiovascular system involve several intracellular events including mitochondrial dysfunction as well as disruption of MAMs. Therefore, an in-depth exploration of the function of MAMs will be of great significance for us to understand the initiation, progression, and clinical complications of cardiovascular disease (CVD). In this review, we summarize the recent advances in our knowledge of MAM regulation and function in CVD-related cells. We discuss the potential roles of MAMs in activating inflammation to influence the development of CVD.

Trimethylamine N-Oxide in Relation to Cardiometabolic Health-Cause or Effect?

Trimethylamine-N-oxide (TMAO) is generated in a microbial-mammalian co-metabolic pathway mainly from the digestion of meat-containing food and dietary quaternary amines such as phosphatidylcholine, choline, betaine, or L-carnitine. Fish intake provides a direct significant source of TMAO. Human observational studies previously reported a positive relationship between plasma TMAO concentrations and cardiometabolic diseases. Discrepancies and inconsistencies of recent investigations and previous studies questioned the role of TMAO in these diseases. Several animal studies reported neutral or even beneficial effects of TMAO or its precursors in cardiovascular disease model systems, supporting the clinically proven beneficial effects of its precursor, L-carnitine, or a sea-food rich diet (naturally containing TMAO) on cardiometabolic health. In this review, we summarize recent preclinical and epidemiological evidence on the effects of TMAO, in order to shed some light on the role of TMAO in cardiometabolic diseases, particularly as related to the microbiome.

Unraveling Host-Gut Microbiota Dialogue and Its Impact on Cholesterol Levels

Disruption in cholesterol metabolism, particularly hypercholesterolemia, is a significant cause of atherosclerotic cardiovascular disease. Large interindividual variations in plasma cholesterol levels are traditionally related to genetic factors, and the remaining portion of their variance is accredited to environmental factors. In recent years, the essential role played by intestinal microbiota in human health and diseases has emerged. The gut microbiota is currently viewed as a fundamental regulator of host metabolism and of innate and adaptive immunity. Its bacterial composition but also the synthesis of multiple molecules resulting from bacterial metabolism vary according to diet, antibiotics, drugs used, and exposure to pollutants and infectious agents. Microbiota modifications induced by recent changes in the human environment thus seem to be a major factor in the current epidemic of metabolic/inflammatory diseases (diabetes mellitus, liver diseases, inflammatory bowel disease, obesity, and dyslipidemia). Epidemiological and preclinical studies report associations between bacterial communities and cholesterolemia. However, such an association remains poorly investigated and characterized. The objectives of this review are to present the current knowledge on and potential mechanisms underlying the host-microbiota dialogue for a better understanding of the contribution of microbial communities to the regulation of cholesterol homeostasis.

Cross-omics analysis revealed gut microbiome-related metabolic pathways underlying atherosclerosis development after antibiotics treatment

Objective

The metabolic influence of gut microbiota plays a pivotal role in the pathogenesis of cardiometabolic diseases. Antibiotics affect intestinal bacterial diversity, and long-term usage has been identified as an independent risk factor for atherosclerosis-driven events. The aim of this study was to explore the interaction between gut dysbiosis by antibiotics and metabolic pathways with the impact on atherosclerosis development.

Methods

We combined oral antibiotics with different diets in an Apolipoprotein E-knockout mouse model linking gut microbiota to atherosclerotic lesion development via an integrative cross-omics approach including serum metabolomics and cecal 16S rRNA targeted metagenomic sequencing. We further investigated patients with carotid atherosclerosis compared to control subjects with comparable cardiovascular risk.

Results

Here, we show that increased atherosclerosis by antibiotics was connected to a loss of intestinal diversity and alterations of microbial metabolic functional capacity with a major impact on the host serum metabolome. Pathways that were modulated by antibiotics and connected to atherosclerosis included diminished tryptophan and disturbed lipid metabolism. These pathways were related to the reduction of certain members of Bacteroidetes and Clostridia by antibiotics in the gut. Patients with atherosclerosis presented a similar metabolic signature as those induced by antibiotics in our mouse model.

Conclusion

Taken together, this work provides insights into the complex interaction between intestinal microbiota and host metabolism. Our data highlight that detrimental effects of antibiotics on the gut flora are connected to a pro-atherogenic metabolic phenotype beyond classical risk factors.

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Antibiotics exacerbate atherosclerosis independently of diet.

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Gut microbiota and metabolic alpha diversity are reduced by antibiotics.

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Pathways connected to atherogenesis are tryptophan and lipid metabolism.

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Metabolic changes are linked to reduced Clostridia and Bacteroidetes in the gut.

Gut microbiota: a promising target against cardiometabolic diseases

Introduction: Cardiometabolic diseases (CMD) are a group of interrelated disorders such as metabolic syndrome, type 2 diabetes mellitus and cardiovascular diseases (CVD). As the prevalence of these diseases increases globally, efficient new strategies are necessary to target CMD and modifiable risk factors. In the past decade, evidence has accumulated regarding the influence of gut microbiota (GM) on CMD, providing new targets for therapeutic interventions.Areas covered: This narrative review discusses the pathophysiologic link between CMD, GM, and potential microbiota-based targets against atherosclerosis and modifiable risk factors for atherosclerosis. Low-grade inflammation can be induced through GM and its derived metabolites. CMD are influenced by GM and microbiota-derived metabolites such as short-chain fatty acids (SCFA), secondary bile acids, trimethylamine N-oxide (TMAO), and the composition of GM can modulate host metabolism. All of the above can lead to promising therapeutic targets.Expert opinion: Most data are derived from animal models or human association studies; therefore, more translational and interventional research in humans is necessary to validate these promising findings. Reproduced findings such as aberrant microbiota patterns or circulating biomarkers could be targeted depending on individual metabolic profiles, moving toward personalized medicine in CMD.

The Gut Microbiota Affects Host Pathophysiology as an Endocrine Organ: A Focus on Cardiovascular Disease

It is widely recognized that the microorganisms inhabiting our gastrointestinal tract-the gut microbiota-deeply affect the pathophysiology of the host. Gut microbiota composition is mostly modulated by diet, and gut microorganisms communicate with the different organs and tissues of the human host by synthesizing hormones and regulating their release. Herein, we will provide an updated review on the most important classes of gut microbiota-derived hormones and their sensing by host receptors, critically discussing their impact on host physiology. Additionally, the debated interplay between microbial hormones and the development of cardiovascular disease will be thoroughly analysed and discussed.

The Microbiota Promotes Arterial Thrombosis in Low-Density Lipoprotein Receptor-Deficient Mice

Atherosclerotic plaque development depends on chronic inflammation of the arterial wall. A dysbiotic gut microbiota can cause low-grade inflammation, and microbiota composition was linked to cardiovascular disease risk. However, the role of this environmental factor in atherothrombosis remains undefined. To analyze the impact of gut microbiota on atherothrombosis, we rederived low-density lipoprotein receptor-deficient (Ldlr^-/- ) mice as germfree (GF) and kept these mice for 16 weeks on an atherogenic high-fat Western diet (HFD) under GF isolator conditions and under conventionally raised specific-pathogen-free conditions (CONV-R). In spite of reduced diversity of the cecal gut microbiome, caused by atherogenic HFD, GF Ldlr^-/- mice and CONV-R Ldlr^-/- mice exhibited atherosclerotic lesions of comparable sizes in the common carotid artery. In contrast to HFD-fed mice, showing no difference in total cholesterol levels, CONV-R Ldlr^-/- mice fed control diet (CD) had significantly reduced total plasma cholesterol, very-low-density lipoprotein (VLDL), and LDL levels compared with GF Ldlr^-/- mice. Myeloid cell counts in blood as well as leukocyte adhesion to the vessel wall at the common carotid artery of GF Ldlr^-/- mice on HFD were diminished compared to CONV-R Ldlr^-/- controls. Plasma cytokine profiling revealed reduced levels of the proinflammatory chemokines CCL7 and CXCL1 in GF Ldlr^-/- mice, whereas the T-cell-related interleukin 9 (IL-9) and IL-27 were elevated. In the atherothrombosis model of ultrasound-induced rupture of the common carotid artery plaque, thrombus area was significantly reduced in GF Ldlr^-/- mice relative to CONV-R Ldlr^-/- mice. Ex vivo, this atherothrombotic phenotype was explained by decreased adhesion-dependent platelet activation and thrombus growth of HFD-fed GF Ldlr^-/- mice on type III collagen.IMPORTANCE Our results demonstrate a functional role for the commensal microbiota in atherothrombosis. In a ferric chloride injury model of the carotid artery, GF C57BL/6J mice had increased occlusion times compared to colonized controls. Interestingly, in late atherosclerosis, HFD-fed GF Ldlr^-/- mice had reduced plaque rupture-induced thrombus growth in the carotid artery and diminished ex vivo thrombus formation under arterial flow conditions.

NLRP3 Inflammasome and the IL-1 Pathway in Atherosclerosis

Inflammation is an important driver of atherosclerosis, the underlying pathology of cardiovascular diseases. Therefore, therapeutic targeting of inflammatory pathways is suggested to improve cardiovascular outcomes in patients with cardiovascular diseases. This concept was recently proven by CANTOS (Canakinumab Anti-Inflammatory Thrombosis Outcomes Study), which demonstrated the therapeutic potential of the monoclonal IL (interleukin)-1β-neutralizing antibody canakinumab. IL-1β and other IL-1 family cytokines are important vascular and systemic inflammatory mediators, which contribute to atherogenesis. The NLRP3 (NOD [nucleotide oligomerization domain]-, LRR [leucine-rich repeat]-, and PYD [pyrin domain]-containing protein 3) inflammasome, an innate immune signaling complex, is the key mediator of IL-1 family cytokine production in atherosclerosis. NLRP3 is activated by various endogenous danger signals abundantly present in atherosclerotic lesions, such as oxidized low-density lipoprotein and cholesterol crystals. Consequently, NLRP3 inflammasome activation contributes to the vascular inflammatory response driving atherosclerosis development and progression. Here, we review the mechanisms of NLRP3 inflammasome activation and proinflammatory IL-1 family cytokine production in the context of atherosclerosis and discuss treatment possibilities in light of the positive outcomes of the CANTOS trial.

Antibiotic Treatment Protocols and Germ-Free Mouse Models in Vascular Research

The gut microbiota influence host vascular physiology locally in the intestine, but also evoke remote effects that impact distant organ functions. Amongst others, the microbiota affect intestinal vascular remodeling, lymphatic development, cardiac output and vascular function, myelopoiesis, prothrombotic platelet function, and immunovigilance of the host. Experimentally, host-microbiota interactions are investigated by working with animals devoid of symbiotic bacteria, i.e., by the decimation of gut commensals by antibiotic administration, or by taking advantage of germ-free mouse isolator technology. Remarkably, some of the vascular effects that were unraveled following antibiotic treatment were not observed in the germ-free animal models and vice versa. In this review, we will dissect the manifold influences that antibiotics have on the cardiovascular system and their effects on thromboinflammation.

Impact of Gut Microbiota and Diet on the Development of Atherosclerosis in Apoe-/- Mice

Objective- To investigate the effect of gut microbiota and diet on atherogenesis. Approach and Results- Here, we investigated the interaction between the gut microbiota and diet on atherosclerosis by feeding germ-free or conventionally raised Apoe-/- mice chow or Western diet alone or supplemented with choline (which is metabolized by the gut microbiota and host enzymes to trimethylamine N-oxide) for 12 weeks. We observed smaller aortic lesions and lower plasma cholesterol levels in conventionally raised mice compared with germ-free mice on a chow diet; these differences were not observed in mice on a Western diet. Choline supplementation increased plasma trimethylamine N-oxide levels in conventionally raised mice but not in germ-free mice. However, this treatment did not affect the size of aortic lesions or plasma cholesterol levels. Gut microbiota composition was analyzed by sequencing of 16S rRNA genes. As expected, the global community structure and relative abundance of many taxa differed between mice fed chow or a Western diet. Choline supplementation had minor effects on the community structure although the relative abundance of some taxa belonging to Clostridiales was altered. Conclusions- In conclusion, the impact of the gut microbiota on atherosclerosis is dietary dependent and is associated with plasma cholesterol levels. Furthermore, the microbiota was required for trimethylamine N-oxide production from dietary choline, but this process could not be linked to increased atherosclerosis in this model.

Cross-Talk between Gut Microbiota and Heart via the Routes of Metabolite and Immunity

Considering the prevalence of cardiovascular disease (CVD), significant interest has been focused on the gut microbiota-heart interaction because the gut microbiota has been recognized as a barometer of human health. Dysbiosis, characterized by changes in the gut microbiota in CVD, has been reported in cardiovascular pathologies, such as atherosclerosis, hypertension, and heart failure. Conversely, gut microbiota-derived metabolites, such as trimethylamine/trimethylamine N-oxide (TMA/TMAO), can impact host physiology. Further, bacterial dysbiosis can disturb gut immunity, which increases the risk of acute arterial events. Moreover, studies of germ-free mice have provided evidence that microbiota diversity and the presence of a specific microbe in the gut can affect immune cells in hosts. Therefore, the changes in the composition of the gut microbiota can affect host metabolism and immunity. Importantly, these effects are not only confined to the gut but also spreaded to distal organs. The purpose of the current review is to highlight the complex interplay between the microbiota and CVD via TMAO and different immune cells and discuss the roles of probiotics and nutrition interventions in modulating the intestinal microbiota as novel therapeutic targets of CVD.

Current State of Knowledge on Implications of Gut Microbiome for Surgical Conditions

The role of the microbiome in human health has become a central tenant of current medical research, infiltrating a diverse disciplinary base whereby microbiology, computer science, ecology, gastroenterology, immunology, neurophysiology and psychology, metabolism, and cardiovascular medicine all intersect. Traditionally, commensal gut microbiota have been assumed to play a significant role only in the metabolic processing of dietary nutrients and host metabolites, the fortification of gut epithelial barrier function, and the development of mucosal immunity. However, over the last 20 years, new technologies and renewed interest have uncovered a considerably broader influence of the microbiota on health maintenance and disease development, many of which are of particular relevance for surgeons. This article provides a broad overview of the current state of knowledge and a review of the technology that helped in their formation.

The gut microbiota as a novel regulator of cardiovascular function and disease

The gut microbiome has emerged as a critical regulator of human physiology. Deleterious changes to the composition or number of gut bacteria, commonly referred to as gut dysbiosis, has been linked to the development and progression of numerous diet-related diseases, including cardiovascular disease (CVD). Most CVD risk factors, including aging, obesity, certain dietary patterns, and a sedentary lifestyle, have been shown to induce gut dysbiosis. Dysbiosis is associated with intestinal inflammation and reduced integrity of the gut barrier, which in turn increases circulating levels of bacterial structural components and microbial metabolites that may facilitate the development of CVD. The aim of the current review is to summarize the available data regarding the role of the gut microbiome in regulating CVD function and disease processes. Particular emphasis is placed on nutrition-related alterations in the microbiome, as well as the underlying cellular mechanisms by which the microbiome may alter CVD risk.

Inflammasome activation by nucleic acids and nucleosomes in sterile inflammation… or is it sterile?

Inflammasomes are multiprotein complexes that form in the cytoplasm in response to cellular damage and cytosolic pathogen-associated molecules during infection. These complexes play important roles in initiating innate and adaptive immune responses to infectious disease. In addition, inflammasomes are now recognized as important mediators of sterile inflammation in various autoimmune and autoinflammatory diseases. Interestingly, microbiota and infection play critical roles in the development of 'sterile inflammation'. Herein, we highlight recent advances in our understanding of the role for inflammasomes in nucleic acid-, nucleosome-, and histone-driven sterile inflammation and discuss knowledge gaps and areas of potential future research.

The immunology of atherosclerosis

Cardiovascular disease is the leading cause of death worldwide, both in the general population and among patients with chronic kidney disease (CKD). In most cases, the underlying cause of the cardiovascular event is atherosclerosis - a chronic inflammatory disease. CKD accelerates atherosclerosis via augmentation of inflammation, perturbation of lipid metabolism, and other mechanisms. In the artery wall, subendothelial retention of plasma lipoproteins triggers monocyte-derived macrophages and T helper type 1 (T_H1) cells to form atherosclerotic plaques. Inflammation is initiated by innate immune reactions to modified lipoproteins and is perpetuated by T_H1 cells that react to autoantigens from the apolipoprotein B100 protein of LDL. Other T cells are also active in atherosclerotic lesions; regulatory T cells inhibit pathological inflammation, whereas T_H17 cells can promote plaque fibrosis. The slow build-up of atherosclerotic plaques is asymptomatic, but plaque rupture or endothelial erosion can induce thrombus formation, leading to myocardial infarction or ischaemic stroke. Targeting risk factors for atherosclerosis has reduced mortality, but a need exists for novel therapies to stabilize plaques and to treat arterial inflammation. Patients with CKD would likely benefit from such preventive measures.

Commensal bacteria at the crossroad between cholesterol homeostasis and chronic inflammation in atherosclerosis

The gut microbiota were shown to play critical roles in the development of atherosclerosis, but the detailed mechanism is limited. The purpose of this study is to clarify the influence of gut microbiota on atherogenesis via lipid metabolism and systemic inflammation. Germ-free or conventionally raised (Conv) ApoE-deficient (ApoE^−/−) mice were fed chow diet and euthanized at 20 weeks of age. We found that the lack of gut microbiota in ApoE^−/− mice caused a significant increase in the plasma and hepatic cholesterol levels compared with Conv ApoE^−/− mice. The absence of gut microbiota changed the bile acid composition in the ileum, which was associated with activation of the enterohepatic fibroblast growth factor 15, fibroblast growth factor receptor 4 axis, and reduction of cholesterol 7α-hydroxylase and hepatic bile acid synthesis, resulting in the accumulation of liver cholesterol content. However, we found that the lack of microbiota caused a significant reduction in atherosclerotic lesion formation compared with Conv ApoE^−/− mice, which might be associated with the attenuation of lipopolysaccharide-mediated inflammatory responses. Our findings indicated that the gut microbiota affected both hypercholesterolemia and atherogenesis in mice.

Intestinal Immunity and Gut Microbiota in Atherogenesis

Atherosclerosis is a chronic inflammatory disease. Interventions targeting the inflammatory process could provide new strategies for preventing atherosclerotic cardiovascular diseases (CVD). Previously, we have reported that oral administration of anti-CD3 antibodies, or active vitamin D₃, reduced atherosclerosis in mice via recruiting regulatory T cells and tolerogenic dendritic cells to the gut-associated lymphoid tissues. From this, it is reasonable to propose that the intestine could be a novel therapeutic target for prevention of atherosclerotic CVD. Recently, the association between cardio-metabolic diseases and gut microbiota has attracted increased attention. Gut microbiota, reported to be highly associated with intestinal immunity and metabolism, were shown to aggravate CVD by contributing to the production of trimethylamine-N-oxide (TMAO), a pro-atherogenic compound. We have also previously investigated the relationship between patient susceptibility to coronary artery disease (CAD) and gut microbiota. We found that the order Lactobacillales was significantly increased and the phylum Bacteroidetes was decreased in CAD patients compared with control patients. In this review article, we discuss the evidence for the relationship between the gut microbiota and cardio-metabolic diseases, and consider the gut microbiota as new potential diagnostic and therapeutic tool for treating CVD.

Role of gut microbiota in atherosclerosis

Infections have been linked to the development of cardiovascular disease and atherosclerosis. Findings from the past decade have identified microbial ecosystems residing in different habitats of the human body that contribute to metabolic and cardiovascular-related disorders. In this Review, we describe three pathways by which microbiota might affect atherogenesis. First, local or distant infections might cause a harmful inflammatory response that aggravates plaque development or triggers plaque rupture. Second, metabolism of cholesterol and lipids by gut microbiota can affect the development of atherosclerotic plaques. Third, diet and specific components that are metabolized by gut microbiota can have various effects on atherosclerosis; for example, dietary fibre is beneficial, whereas the bacterial metabolite trimethylamine-N-oxide is considered harmful. Although specific bacterial taxa have been associated with atherosclerosis, which is supported by increasing mechanistic evidence, several questions remain to be answered to understand fully how the microbiota contributes to atherosclerosis and cardiovascular disease. Such knowledge might pave the way for novel diagnostics and therapeutics based on microbiota.

Complement activation by cholesterol crystals triggers a subsequent cytokine response

In the host a diverse collection of endogenous danger signals is constantly generated consisting of waste material as protein aggregates or crystalline materials that are recognized and handled by soluble pattern recognition receptors and phagocytic cells of the innate immune system. These signals may under certain circumstances drive processes leading to adverse inflammation. One example is cholesterol crystals (CC) that accumulate in the vessel wall during early phases of atherogenesis and represent an important endogenous danger signal promoting inflammation. CC is recognized by the lectin- and classical pathways of the complement system resulting in activation of C3 and C5 with release of inflammatory mediators like the potent C5a fragment. Complement activation by CC leads to crosstalk with the NLRP3 inflammasome-caspase-1 pathway and production of IL-1β. Neutralization of IL-1β may have beneficial effects on atherosclerosis and a large clinical trial with an IL-1β inhibitor is currently in progress (the CANTOS study). However, upstream inhibition of CC-induced inflammation by using a complement inhibitor may be more efficient in treating atherosclerosis since this will block initiation of inflammation processes before downstream release of cytokines including IL-1β. Another therapeutic candidate can be broad-acting 2-hydroxypropyl-β-cyclodextrin, a compound that targets several mechanisms such as cholesterol efflux, complement gene expression, and the NLRP3 pathway. In summary, emerging evidence show that complement is a key upstream player in the pathophysiology of atherosclerosis and that therapy aiming at inhibiting complement could be effective in controlling atherosclerosis.

Akkermansia Muciniphila Protects Against Atherosclerosis by Preventing Metabolic Endotoxemia-Induced Inflammation in Apoe-/- Mice

BACKGROUND

Altered composition of the gut microbiota is involved in both the onset and progression of obesity and diabetes mellitus. However, the link between gut microbiota and obesity-related cardiovascular complications has not been explored. The present study was designed to investigate the role of Akkermansia muciniphila, a mucin-degrading bacterium with beneficial effects on metabolism, in the pathogenesis of atherosclerosis in apolipoprotein E-deficient (Apoe(-/-)) mice.

METHODS AND RESULTS

Apoe(-/-) mice on normal chow diet or a Western diet were treated with A muciniphila by daily oral gavage for 8 weeks, followed by histological evaluations of atherosclerotic lesion in aorta. Real-time polymerase chain reaction analysis demonstrated that the fecal abundance of A muciniphila was significantly reduced by Western diet. Replenishment with A muciniphila reversed Western diet-induced exacerbation of atherosclerotic lesion formation without affecting hypercholesterolemia. A muciniphila prevented Western diet-induced inflammation in both the circulation and local atherosclerotic lesion, as evidenced by reduced macrophage infiltration and expression of proinflammatory cytokines and chemokines. These changes were accompanied by a marked attenuation in metabolic endotoxemia. A muciniphila-mediated reduction in circulating endotoxin level could be attributed to the induction of intestinal expression of the tight junction proteins (zona occuldens protein-1 and occludin), thereby reversing Western diet-induced increases in gut permeability. Long-term infusion of endotoxin to Apoe(-/-) mice reversed the protective effect of A muciniphila against atherosclerosis.

CONCLUSION

A muciniphila attenuates atherosclerotic lesions by ameliorating metabolic endotoxemia-induced inflammation through restoration of the gut barrier.

Role of Nucleotide-binding and Oligomerization Domain 2 Protein (NOD2) in the Development of Atherosclerosis

NOD2 (nucleotide-binding and oligomerization domain 2) was initially reported as a susceptibility gene for Crohn's disease, with several studies focused on elucidating its molecular mechanism in the progression of Crohn's disease. We now know that NOD2 is an intracellular bacterial sensing receptor, and that MDP-mediated NOD2 activation drives inflammatory signaling. Various mutations in NOD2 have been reported, with NOD2 loss of function being associated with the development of Crohn's disease and other autoimmune diseases. These results suggest that NOD2 not only has an immune stimulatory function, but also an immune regulatory function. Atherosclerosis is a chronic inflammatory disease of the arterial wall; its pathologic progression is highly dependent on the immune balance. This immune balance is regulated by infiltrating monocytes and macrophages, both of which express NOD2. These findings indicate a potential role of NOD2 in atherosclerosis. The purpose of this review is to outline the known roles of NOD2 signaling in the pathogenesis of atherosclerosis.

Unraveling the environmental and genetic interactions in atherosclerosis: Central role of the gut microbiota

Recent studies have convincingly linked gut microbiota to traits relevant to atherosclerosis, such as insulin resistance, dyslipidemia and inflammation, and have revealed novel disease pathways involving microbe-derived metabolites. These results have important implications for understanding how environmental and genetic factors act together to influence cardiovascular disease (CVD) risk. Thus, dietary constituents are not only absorbed and metabolized by the host but they also perturb the gut microbiota, which in turn influence host metabolism and inflammation. It also appears that host genetics helps to shape the gut microbiota community. Here, we discuss challenges in understanding these interactions and the role they play in CVD.

Human Microbiome: When a Friend Becomes an Enemy

The microorganisms that inhabit humans are very diverse on different body sites and tracts. Each specific niche contains a unique composition of the microorganisms that are important for a balanced human physiology. Microbial cells outnumber human cells by tenfold and they function as an invisible organ that is called the microbiome. Excessive use of antibiotics and unhealthy diets pose a serious danger to the composition of the microbiome. An imbalance in the microbial community may cause pathological conditions of the digestive system such as obesity, cancer and inflammatory bowel disease; of the skin such as atopic dermatitis, psoriasis and acne and of the cardiovascular system such as atherosclerosis. An unbalanced microbiome has also been associated with neurodevelopmental disorders such as autism and multiple sclerosis. While the microbiome has a strong impact on the development of the host immune system, it is suspected that it can also be the cause of certain autoimmune diseases, including diabetes or rheumatoid arthritis. Despite the enormous progress in the field, the interactions between the human body and its microbiome still remain largely unknown. A better characterization of the interactions may allow for a deeper understanding of human disease states and help to elucidate a possible association between the composition of the microbiome and certain pathologies. This review focuses on general findings that are related to the area and provides no detailed information about the case of study. The aim is to give some initial insight on the studies of the microbiome and its connection with human health.

Intestinal Immunity and Gut Microbiota as Therapeutic Targets for Preventing Atherosclerotic Cardiovascular Diseases

Atherosclerosis is considered a chronic inflammatory disease and an intervention targeting the inflammatory process could be a new therapeutic strategy for preventing atherosclerotic cardiovascular diseases (CVD). We hypothesized that the intestine, which is considered the biggest immune organ in the human body, could be a therapeutic target for preventing CVD. We demonstrated that oral administration of anti-CD3 antibody or an active form of vitamin D3 reduced atherosclerosis in mice via induction of regulatory T cells and tolerogenic dendritic cells in the gut-associated lymphoid tissues. Similar to regulatory immune responses achieved by oral tolerance, our method had systemic effects that ultimately contributed towards atherosclerosis reduction. Recently, we have been interested in the gut microbiota, which have been reported as highly associated with intestinal immunity and systemic metabolic disorders, including obesity and diabetes. Notably, the guts of obese individuals are predominantly colonized by Firmicutes over Bacteroidetes. The association between atherosclerosis and microbiota has been attracting increased attention, and gut microbiota have been shown to participate in the metabolism of a proatherogenic compound called trimethylamine-N-oxide (TMAO) and aggravate CVD. Our investigation of the relationship between susceptibility to CVD and the gut microbiota revealed a characteristic flora type. Here, we discuss the evidence for the relationship between the gut microbiota and cardiometabolic diseases, and consider the gut microbiota as new potential therapeutic targets for treating CVD. (Circ J 2015; 79: 1882-1890).

Drivers of age-related inflammation and strategies for healthspan extension

Aging is the greatest risk factor for the development of chronic diseases such as arthritis, type 2 diabetes, cardiovascular disease, kidney disease, Alzheimer's disease, macular degeneration, frailty, and certain forms of cancers. It is widely regarded that chronic inflammation may be a common link in all these age-related diseases. This raises the question, can one alter the course of aging and potentially slow the development of all chronic diseases by manipulating the mechanisms that cause age-related inflammation? Emerging evidence suggests that pro-inflammatory cytokines interleukin-1 (IL-1) and IL-18 show an age-dependent regulation implicating inflammasome-mediated caspase-1 activation in the aging process. The Nod-like receptor (NLR) family of innate immune cell sensors, such as the nucleotide-binding domain, leucine-rich-containing family, pyrin domain-containing-3 (NLRP3) inflammasome controls the caspase-1 activation in myeloid-lineage cells in several organs during aging. The NLRP3 inflammasome is especially relevant to aging as it can get activated in response to structurally diverse damage-associated molecular patterns (DAMPs) such as extracellular ATP, excess glucose, ceramides, amyloids, urate, and cholesterol crystals, all of which increase with age. Interestingly, reduction in NLRP3-mediated inflammation prevents age-related insulin resistance, bone loss, cognitive decline, and frailty. NLRP3 is a major driver of age-related inflammation and therefore dietary or pharmacological approaches to lower aberrant inflammasome activation holds promise in reducing multiple chronic diseases of age and may enhance healthspan.

Helicobacter pylori vs coronary heart disease - searching for connections

In this review, we discussed the findings and concepts underlying the potential role of Helicobacter pylori (H. pylori) infections in the initiation, development or persistence of atherosclerosis and coronary heart disease (CHD). This Gram-negative bacterium was described by Marshall and Warren in 1984. The majority of infected subjects carries and transmits H. pylori with no symptoms; however, in some individuals these bacteria may cause peptic ulcers, and even gastric cancers. The widespread prevalence of H. pylori infections and the fact that frequently they remain asymptomatic may suggest that, similarly to intestinal microflora, H. pylori may deliver antigens that stimulate not only local, but also systemic inflammatory response. Recently, possible association between H. pylori infection and extragastric disorders has been suggested. Knowledge on the etiology of atherosclerosis together with current findings in the area of H. pylori infections constitute the background for the newly proposed hypothesis that those two processes may be related. Many research studies confirm the indirect association between the prevalence of H. pylori and the occurrence of CHD. According to majority of findings the involvement of H. pylori in this process is based on the chronic inflammation which might facilitate the CHD-related pathologies. It needs to be elucidated, if the infection initiates or just accelerates the formation of atheromatous plaque.

Danger signaling in atherosclerosis

All aspects of the pathogenesis of atherosclerosis are critically influenced by the inflammatory response in vascular plaques. Research in the field of innate immunity from the past 2 decades has uncovered many novel mechanisms elucidating how immune cells sense microbes, tissue damage, and metabolic derangements. Here, we summarize which triggers of innate immunity appear during atherogenesis and by which pathways they can contribute to inflammation in atherosclerotic plaques. The increased understanding gained from studies assessing how immune activation is associated with the pathogenesis of atherosclerosis has provided many novel targets for potential therapeutic intervention. Excitingly, the concept that inflammation may be the core of cardiovascular disease is currently being clinically evaluated and will probably encourage further studies in this area.

The inflammasomes and autoinflammatory syndromes

Inflammation, a vital response of the immune system to infection and damage to tissues, can be initiated by various germline-encoded innate immune-signaling receptors. Among these, the inflammasomes are critical for activation of the potent proinflammatory interleukin-1 cytokine family. Additionally, inflammasomes can trigger and maintain inflammatory responses aimed toward excess nutrients and the numerous danger signals that appear in a variety of chronic inflammatory diseases. We discuss our understanding of how inflammasomes assemble to trigger caspase-1 activation and subsequent cytokine release, describe how genetic mutations in inflammasome-related genes lead to autoinflammatory syndromes, and review the contribution of inflammasome activation to various pathologies arising from metabolic dysfunction. Insights into the mechanisms that govern inflammasome activation will help in the development of novel therapeutic strategies, not only for managing genetic diseases associated with overactive inflammasomes, but also for treating common metabolic diseases for which effective therapies are currently lacking.

Far from the eyes, close to the heart: dysbiosis of gut microbiota and cardiovascular consequences

These days, the gut microbiota is universally recognized as an active organ that can modulate the overall host metabolism by promoting multiple functions, from digestion to the systemic maintenance of overall host physiology. Dysbiosis, the alteration of the complex ecologic system of gut microbes, is associated with and causally responsible for multiple types of pathologies. Among the latters, metabolic diseases such as type 2 diabetes and obesity are each distinguishable by a unique gut microbiota profile. Interestingly, the specific microbiota typically found in the blood of diabetic patients also has been observed at the level of atherosclerotic plaque. Here, we report evidence from the literature, as well as a few controversial reports, regarding the putative role of gut microbiota dysbiosis-induced cardiovascular diseases, such as atherosclerosis, which are common comorbidities of metabolic dysfunction.

Inflammasomes and metabolic disorders: old genes in modern diseases

Modern medical and hygienic practices have greatly improved human health and longevity; however, increased human life span occurs concomitantly with the emergence of metabolic and age-related diseases. Studies over the past decade have strongly linked host inflammatory responses to the etiology of several metabolic diseases including atherosclerosis, type 2 diabetes (T2D), obesity, and gout. A common immunological factor to these diseases is the activation of the inflammasome and release of proinflammatory cytokines that promote disease progression. Here we review the molecular mechanism(s) of inflammasome activation in response to metabolic damage-associated molecular patterns (DAMPs) and discuss potential targets for therapeutic intervention.

Toll-like receptor, lipotoxicity and chronic inflammation: the pathological link between obesity and cardiometabolic disease

The epidemic growth in the prevalence of obesity has made the impact of metabolic syndrome on cardiovascular events increasingly significant. Elevated visceral adiposity, the indispensable component of metabolic syndrome, is thought to play a primary role in the increasing incidence of cardiometabolic disorders. Importantly, obesity is not merely the simple expansion of adipose tissue mass; it also involves the activation of inflammatory processes within visceral adipose tissue. Adipose tissue inflammation on the one hand enhances the production of proinflammatory adipokines and on the other hand increases the release of free fatty acids via the activation of lipolysis. The adipokines and free fatty acids secreted from visceral fat then contribute to a cardiometabolic pathology. We herein summarize recent advances in our understanding of the mechanisms by which visceral obesity leads to the activation of inflammation in cardiovascular and metabolic tissues and promotes cardiometabolic disease. Our focus is on Toll-like receptor 4 signaling and free fatty acids as mediators of chronic inflammation in patients with metabolic syndrome and atherosclerosis.

Atherosclerosis and Alzheimer--diseases with a common cause? Inflammation, oxysterols, vasculature

BACKGROUND

Aging is accompanied by increasing vulnerability to pathologies such as atherosclerosis (ATH) and Alzheimer disease (AD). Are these different pathologies, or different presentations with a similar underlying pathoetiology?

DISCUSSION

Both ATH and AD involve inflammation, macrophage infiltration, and occlusion of the vasculature. Allelic variants in common genes including APOE predispose to both diseases. In both there is strong evidence of disease association with viral and bacterial pathogens including herpes simplex and Chlamydophila. Furthermore, ablation of components of the immune system (or of bone marrow-derived macrophages alone) in animal models restricts disease development in both cases, arguing that both are accentuated by inflammatory/immune pathways. We discuss that amyloid β, a distinguishing feature of AD, also plays a key role in ATH. Several drugs, at least in mouse models, are effective in preventing the development of both ATH and AD. Given similar age-dependence, genetic underpinnings, involvement of the vasculature, association with infection, Aβ involvement, the central role of macrophages, and drug overlap, we conclude that the two conditions reflect different manifestations of a common pathoetiology.

MECHANISM

Infection and inflammation selectively induce the expression of cholesterol 25-hydroxylase (CH25H). Acutely, the production of 'immunosterol' 25-hydroxycholesterol (25OHC) defends against enveloped viruses. We present evidence that chronic macrophage CH25H upregulation leads to catalyzed esterification of sterols via 25OHC-driven allosteric activation of ACAT (acyl-CoA cholesterol acyltransferase/SOAT), intracellular accumulation of cholesteryl esters and lipid droplets, vascular occlusion, and overt disease.

SUMMARY

We postulate that AD and ATH are both caused by chronic immunologic challenge that induces CH25H expression and protection against particular infectious agents, but at the expense of longer-term pathology.

Amide-adducts in atherosclerosis

Too many hypotheses in the etiology of atherosclerosis have been proposed. Classically, lipid insudation hypothesis by Virchow and thrombogenic hypothesis by Rokitansky are famous. However, in the recent progress in the area of atherosclerosis, the response-to-injury hypothesis by Ross (Ross R Glomset JA, N Engl J Med 295:369-377, 420-425, 1976; Ross R, Arteriosclerosis 1:293-311, 1981; Ross R, N Engl J Med 314:488-500, 1986; Ross R, Nature 362:801-809, 1993; Ross R, N Engl J Med 340:115-126, 1999) has been the leading one. In this review, however, the author focuses to the recent debate on the role of oxidative modification of atherogenic lipoproteins.