Cytokines induce indoleamine 2,3-dioxygenase expression in human atheroma-asociated cells: implications for persistent Chlamydophila pneumoniae infection

Evolving concepts in the pathophysiology of atherosclerosis: from endothelial dysfunction to thrombus formation through multiple shades of inflammation

Atherosclerosis is the anatomo-pathological substrate of most cardio, cerebro and vascular diseases such as acute and chronic coronary syndromes, stroke and peripheral artery diseases. The pathophysiology of atherosclerotic plaque and its complications are under continuous investigation. In the last 2 decades our understanding on the formation, progression and complication of the atherosclerotic lesion has greatly improved and the role of immunity and inflammation is now well documented and accepted. The conventional risk factors modulate endothelial function determining the switch to a proatherosclerotic phenotype. From this point, lipid accumulation with an imbalance from cholesterol influx and efflux, foam cells formation, T-cell activation, cytokines release and matrix-degrading enzymes production occur. Lesions with high inflammatory rate become vulnerable and prone to rupture. Once complicated, the intraplaque thrombogenic material, such as the tissue factor, is exposed to the flowing blood, thus inducing coagulation cascade activation, platelets aggregation and finally intravascular thrombus formation that leads to clinical manifestations of this disease. Nonconventional risk factors, such as gut microbiome, are emerging novel markers of atherosclerosis. Several data indicate that gut microbiota may play a causative role in formation, progression and complication of atherosclerotic lesions. The gut dysbiosis-related inflammation and gut microbiota-derived metabolites have been proposed as the main working hypothesis in contributing to disease formation and progression. The current evidence suggest that the conventional and nonconventional risk factors may modulate the degree of inflammation of the atherosclerotic lesion, thus influencing its final fate. Based on this hypothesis, targeting inflammation seems to be a promising approach to further improve our management of atherosclerotic-related diseases.

Identification of Biomarkers for the Diagnosis of Sepsis-Associated Acute Kidney Injury and Prediction of Renal Recovery in the Intensive Care Unit

PURPOSE

Acute kidney injury (AKI) following sepsis is associated with higher mortality; however, reliable biomarkers for AKI development and recovery remain to be elucidated.

MATERIALS AND METHODS

Patients with sepsis admitted to the medical intensive care unit (ICU) of Severance Hospital between June 2018 and May 2019 were prospectively analyzed. Patients were divided into those with and without AKI within 48 hours. Patients with septic AKI were subdivided into AKI-recovery and non-recovery groups based on whether their kidney injury recovered within 7 days.

RESULTS

A total of 84 patients were enrolled. The baseline creatinine (2.9 mg/dL vs. 0.8 mg/dL vs. 1.2 mg/dL, p<0.001), Charlson Comorbidity Index (4.5 vs. 2.0 vs. 3.0, p=0.002), Sequential Organ Failure Assessment (10.0 vs. 6.5 vs. 8.0, p<0.001), and Acute Physiology and Chronic Health Evaluation II scores (32.0 vs. 21.5 vs. 30.5, p=0.004) were higher in the non-recovery AKI group compared to the non-AKI and AKI-recovery groups. The Kaplan-Meier curves revealed that non-recovery from AKI was associated with lower survival (p<0.001). High-lactate (p≤0.05) and kynurenine levels (p≤0.05) were associated with non-recovery of renal function following AKI. The areas under the curve for predicting non-recovery from AKI were 0.693 and 0.721 for lactate and kynurenine, respectively. The survival rate was lower in the high-kynurenine (p=0.040) and high-lactate (p=0.010) groups.

CONCLUSION

The mortality of patients who recovered from AKI was comparable to that of patients without AKI. Lactate and kynurenine could be useful biomarkers for the diagnosis and recovery of AKI following sepsis.

Ubiquitylome study reveals the regulatory effect of α-lipoic acid on ubiquitination of key proteins in tryptophan metabolism pathway of pig liver

The decline in antioxidant defenses make it easily for human and animals to suffer from liver damage and diseases induced by oxidative stress, causing enormous losses to human health and livestock production. As one of the canonical protein post-translational modifications (PTMs), ubiquitination is widely involved in cell proliferation, apoptosis and damage/repair response, and is proven to be involved in the ability of mammals to resist oxidative stress. To explore whether α-lipoic acid (LA), a safe and efficient antioxidant, plays a role in regulating liver antioxidant status by PTMs, proteins in livers of pigs fed with LA were analyzed at the level of proteome and ubiquitylome. Based on proteome-wide enrichment of ubiquitination, a total of 7274 proteins were identified and 5326 were quantified, we also identified 1564 ubiquitination sites in 580 ubiquitinated proteins, among which there were 136 differentially ubiquitinated sites in 103 differentially ubiquitinated proteins upon LA. Further bioinformatics analysis showed that these differential proteins were mainly enriched in tryptophan metabolic pathway, and accompanied by significantly improvement of liver antioxidant capacity. We revealed the regulatory effect of LA on ubiquitination of kynurenine 3-monooxygenase (KMO) and other key proteins in tryptophan metabolism pathway of pig liver for the first time.

The Probable Role of Chlamydia pneumoniae Infection in Acute Stroke

Cardiovascular diseases are the most leading cause of worldwide mortality. According to USA statistics, about 1 of 6 cardiovascular deaths is due to stroke. Stroke is the second most common cause of death and a chief cause of disability due to EU data. Treatment, care providing, rehabilitation costs and with the labor loss, the overall cost in EU due to stroke was estimated about €45 billion in year 2017. Acute stroke due to infectious diseases via several possible mechanisms with various clinical presentations were previously reported in the literature. Chlamydia pneumoniae is an obligate intracellular bacteria and extremely common in adult individuals. Besides it being a major cause of pneumonia in adults, association between atherosclerosis and vascular diseases was demonstrated by several sero-epidemiological studies and by direct detection of organism in atherosclerotic lesions by electron microscopy, immunohistochemistry, polymerase chain reaction. Also, several sero-epidemiological studies have demonstrated a link between Chlamydia pneumoniae infection and acute stroke. In this chapter, we will summarize the data in literature regarding the association between Chlamydia pneumoniae infection and acute stroke and we will try to explain the possible mechanisms that could be responsible in pathophysiology of stroke in these patients.

Kynurenine Pathway Metabolites as Potential Clinical Biomarkers in Coronary Artery Disease

Coronary artery disease (CAD) is one of the leading cause of mortality worldwide. Several risk factors including unhealthy lifestyle, genetic background, obesity, diabetes, hypercholesterolemia, hypertension, smoking, age, etc. contribute to the development of coronary atherosclerosis and subsequent coronary artery disease. Inflammation plays an important role in coronary artery disease development and progression. Pro-inflammatory signals promote the degradation of tryptophan via the kynurenine pathway resulting in the formation of several immunomodulatory metabolites. An unbalanced kynurenic pathway has been implicated in the pathomechanisms of various diseases including CAD. Significant improvements in detection methods in the last decades may allow simultaneous measurement of multiple metabolites of the kynurenine pathway and such a thorough analysis of the kynurenine pathway may be a valuable tool for risk stratification and determination of CAD prognosis. Nevertheless, imbalance in the activities of different branches of the kynurenine pathway may require careful interpretation. In this review, we aim to summarize clinical evidence supporting a possible use of kynurenine pathway metabolites as clinical biomarkers in various manifestations of CAD.

Emerging Roles on Immunological Effect of Indoleamine 2,3-Dioxygenase in Liver Injuries

Indoleamine 2,3-dioxygenase (IDO) is one of the initial rate-limiting enzymes of the kynurenine pathway (KP), which causes immune suppression and induction of T cell anergy. It is associated with the imbalance of immune homeostasis in numerous diseases including cancer, chronic viral infection, allergy, and autoimmune diseases. Recently, IDO has extended its role to liver field. In this review, we summarize the dysregulation and potentials of IDO in the emerging field of liver injuries, as well as current challenges for IDO targets. In particular, we discuss unexpected conclusions against previous work published. IDO is induced by pro-inflammatory cytokines in liver dysfunction and exerts an immunosuppressive effect, whereas the improvement of liver injury may require consideration of multiple factors besides IDO.

Interferon-γ Impairs Human Coronary Artery Endothelial Glucose Metabolism by Tryptophan Catabolism and Activates Fatty Acid Oxidation

BACKGROUND

Endothelial cells depend on glycolysis for much of their energy production. Impaired endothelial glycolysis has been associated with various vascular pathobiologies, including impaired angiogenesis and atherogenesis. IFN-γ (interferon-γ)-producing CD4⁺ and CD8⁺ T lymphocytes have been identified as the predominant pathological cell subsets in human atherosclerotic plaques. Although the immunologic consequences of these cells have been extensively evaluated, their IFN-γ-mediated metabolic effects on endothelial cells remain unknown. The purpose of this study was to determine the metabolic consequences of the T-lymphocyte cytokine, IFN-γ, on human coronary artery endothelial cells.

METHODS

The metabolic effects of IFN-γ on primary human coronary artery endothelial cells were assessed by unbiased transcriptomic and metabolomic analyses combined with real-time extracellular flux analyses and molecular mechanistic studies. Cellular phenotypic correlations were made by measuring altered endothelial intracellular cGMP content, wound-healing capacity, and adhesion molecule expression.

RESULTS

IFN-γ exposure inhibited basal glycolysis of quiescent primary human coronary artery endothelial cells by 20% through the global transcriptional suppression of glycolytic enzymes resulting from decreased basal HIF1α (hypoxia-inducible factor 1α) nuclear availability in normoxia. The decrease in HIF1α activity was a consequence of IFN-γ-induced tryptophan catabolism resulting in ARNT (aryl hydrocarbon receptor nuclear translocator)/HIF1β sequestration by the kynurenine-activated AHR (aryl hydrocarbon receptor). In addition, IFN-γ resulted in a 23% depletion of intracellular nicotinamide adenine dinucleotide in human coronary artery endothelial cells. This altered glucose metabolism was met with concomitant activation of fatty acid oxidation, which augmented its contribution to intracellular ATP balance by >20%. These metabolic derangements were associated with adverse endothelial phenotypic changes, including decreased basal intracellular cGMP, impaired endothelial migration, and a switch to a proinflammatory state.

CONCLUSIONS

IFN-γ impairs endothelial glucose metabolism by altered tryptophan catabolism destabilizing HIF1, depletes nicotinamide adenine dinucleotide, and results in a metabolic shift toward increased fatty acid oxidation. This work suggests a novel mechanistic basis for pathological T lymphocyte-endothelial interactions in atherosclerosis mediated by IFN-γ, linking endothelial glucose, tryptophan, and fatty acid metabolism with the nicotinamide adenine dinucleotide balance and ATP generation and their adverse endothelial functional consequences.

Crosstalk between Tryptophan Metabolism via Kynurenine Pathway and Carbohydrate Metabolism in the Context of Cardio-Metabolic Risk-Review

Scientific interest in tryptophan metabolism via the kynurenine pathway (KP) has increased in the last decades. Describing its metabolites helped to increase their roles in many diseases and disturbances, many of a pro-inflammatory nature. It has become increasingly evident that KP can be considered an important part of emerging mediators of diabetes mellitus and metabolic syndrome (MS), mostly stemming from chronic systemic low-grade inflammation resulting in the aggravation of cardiovascular complications. An electronic literature search of PubMed and Embase up to March 2021 was performed for papers reporting the effects of tryptophan (TRP), kynurenine (KYN), kynurenic acid (KYNA), xanthurenic acid (XA), anthranilic acid (AA), and quinolinic acid (QA), focusing on their roles in carbohydrate metabolism and the cardiovascular system. In this review, we discussed the progress in tryptophan metabolism via KP research, focusing particular attention on the roles in carbohydrate metabolism and its complications in the cardiovascular system. We examined the association between KP and diabetes mellitus type 2 (T2D), diabetes mellitus type 1 (T1D), and cardiovascular diseases (CVD). We concluded that tryptophan metabolism via KP serves as a potential diagnostic tool in assessing cardiometabolic risk for patients with T2D.

The changing landscape of atherosclerosis

Emerging evidence has spurred a considerable evolution of concepts relating to atherosclerosis, and has called into question many previous notions. Here I review this evidence, and discuss its implications for understanding of atherosclerosis. The risk of developing atherosclerosis is no longer concentrated in Western countries, and it is instead involved in the majority of deaths worldwide. Atherosclerosis now affects younger people, and more women and individuals from a diverse range of ethnic backgrounds, than was formerly the case. The risk factor profile has shifted as levels of low-density lipoprotein (LDL) cholesterol, blood pressure and smoking have decreased. Recent research has challenged the protective effects of high-density lipoprotein, and now focuses on triglyceride-rich lipoproteins in addition to low-density lipoprotein as causal in atherosclerosis. Non-traditional drivers of atherosclerosis-such as disturbed sleep, physical inactivity, the microbiome, air pollution and environmental stress-have also gained attention. Inflammatory pathways and leukocytes link traditional and emerging risk factors alike to the altered behaviour of arterial wall cells. Probing the pathogenesis of atherosclerosis has highlighted the role of the bone marrow: somatic mutations in stem cells can cause clonal haematopoiesis, which represents a previously unrecognized but common and potent age-related contributor to the risk of developing cardiovascular disease. Characterizations of the mechanisms that underpin thrombotic complications of atherosclerosis have evolved beyond the 'vulnerable plaque' concept. These advances in our understanding of the biology of atherosclerosis have opened avenues to therapeutic interventions that promise to improve the prevention and treatment of now-ubiquitous atherosclerotic diseases.

Identification of biomarkers for essential hypertension based on metabolomics

AIM

Essential hypertension (EH) is one of the most important public health problems worldwide. However, the pathogenesis of EH is unclear and early diagnostic methods are lacking. Metabolomics demonstrates great potential for biomarker discovery and the mechanistic exploration of metabolic diseases.

DATA SYNTHESIS

This review included human and animal metabolomics studies related to EH in the PubMed and Web of Science databases between February 1996 and May 2020. The study designs, EH standards, and reported metabolic biomarkers were systematically examined and compared. The pathway analysis was conducted through the online software MetaboAnalyst 4.0. Twenty-two human studies and fifteen animal studies were included in this systematic review. There were many frequently reported biomarkers with consistent trends (e.g., pyruvate, lactic acid, valine, and tryptophan) in human and animal studies, and thus had potential as biomarkers of EH. In addition, several shared metabolic pathways, including alanine, aspartate, and glutamate metabolism, aminoacyl-tRNA biosynthesis, and arginine biosynthesis, were identified in human and animal metabolomics studies. These biomarkers and pathways, closely related to insulin resistance, the inflammatory state, and impaired nitric oxide production, were demonstrated to contribute to EH development.

CONCLUSIONS

This study summarized valuable metabolic biomarkers and pathways that could offer opportunities for the early diagnosis or prediction of EH and the discovery of the metabolic mechanisms of EH.

Atherosclerosis Linked to Aberrant Amino Acid Metabolism and Immunosuppressive Amino Acid Catabolizing Enzymes

Cardiovascular disease is the leading global health concern and responsible for more deaths worldwide than any other type of disorder. Atherosclerosis is a chronic inflammatory disease in the arterial wall, which underpins several types of cardiovascular disease. It has emerged that a strong relationship exists between alterations in amino acid (AA) metabolism and the development of atherosclerosis. Recent studies have reported positive correlations between levels of branched-chain amino acids (BCAAs) such as leucine, valine, and isoleucine in plasma and the occurrence of metabolic disturbances. Elevated serum levels of BCAAs indicate a high cardiometabolic risk. Thus, BCAAs may also impact atherosclerosis prevention and offer a novel therapeutic strategy for specific individuals at risk of coronary events. The metabolism of AAs, such as L-arginine, homoarginine, and L-tryptophan, is recognized as a critical regulator of vascular homeostasis. Dietary intake of homoarginine, taurine, and glycine can improve atherosclerosis by endothelium remodeling. Available data also suggest that the regulation of AA metabolism by indoleamine 2,3-dioxygenase (IDO) and arginases 1 and 2 are mediated through various immunological signals and that immunosuppressive AA metabolizing enzymes are promising therapeutic targets against atherosclerosis. Further clinical studies and basic studies that make use of animal models are required. Here we review recent data examining links between AA metabolism and the development of atherosclerosis.

The immunometabolic role of indoleamine 2,3-dioxygenase in atherosclerotic cardiovascular disease: immune homeostatic mechanisms in the artery wall

Coronary heart disease and stroke, the two most common cardiovascular diseases worldwide, are triggered by complications of atherosclerosis. Atherosclerotic plaques are initiated by a maladaptive immune response triggered by accumulation of lipids in the artery wall. Hence, disease is influenced by several non-modifiable and modifiable risk factors, including dyslipidaemia, hypertension, smoking, and diabetes. Indoleamine 2,3-dioxygenase (IDO), the rate-limiting enzyme in the kynurenine pathway of tryptophan (Trp) degradation, is modulated by inflammation and regarded as a key molecule driving immunotolerance and immunosuppressive mechanisms. A large body of evidence indicates that IDO-mediated Trp metabolism is involved directly or indirectly in atherogenesis. This review summarizes evidence from basic and clinical research showing that IDO is a major regulatory enzyme involved in the maintenance of immunohomeostasis in the vascular wall, as well as current knowledge about promising targets for the development of new anti-atherosclerotic drugs.

Grey and white matter structure associates with the activation of the tryptophan to kynurenine pathway in bipolar disorder

BACKGROUND

Bipolar disorder (BD) is a severe mental illness characterised by reduced grey matter (GM) volumes and cortical thickness, and disrupted white matter (WM) microstructure. Activation of indoleamine 2,3-dioxygenase following a pro-inflammatory state could increase the amount of tryptophan (Trp) converted to kynurenine (Kyn) possibly leading to the production of detrimental catabolites of the Kyn pathway with neurotoxic effects. We investigated if peripheral levels of Trp-and Kyn and the breakdown of Trp-into Kyn (Kyn/Trp-ratio) are related to WM and GM integrity in BD.

METHODS

Peripheral levels of Trp-and Kyn were analysed in 72 patients with BD and 33 controls. Patients also underwent MRI in a Philips 3T scanner.

RESULTS

Patients showed higher Kyn levels and Kyn/Trp-ratio compared to controls. MRI analyses performed in patients with BD showed a negative association between the Kyn/Trp-ratio and the integrity of corpus callosum microstructure, the volume of the amygdala and cortical thickness in fronto-parietal regions.

LIMITATION

The lack of information on the levels of downstream metabolites of Kyn prevent us to confirm the possible unbalance between quinolinic and kynurenic acids as well as their possible relationship with changes in GM and WM markers. The activation of the Kyn pathway as suggested by the increased Kyn/Trp-ratio may lead to an imbalance of the neurotoxic vs the neuroprotective arm of the biochemical pathway, resulting in significant changes in GM and WM regions of brain areas strongly implicated in the pathophysiology of BD, such as amygdala and corpus callosum.

Kynurenine pathway and white matter microstructure in bipolar disorder

Decreased availability of serotonin in the central nervous system has been suggested to be a central factor in the pathogenesis of depression. Activation of indoleamine 2-3 dioxygenase following a pro-inflammatory state could reduce the amount of tryptophan converted to serotonin and increase the production of tryptophan catabolites such as kynurenic acid, an antagonist of ionotropic excitatory aminoacid receptors, whose levels are reduced in bipolar disorder. Abnormalities in white matter (WM) integrity have been widely reported in BD. We then hypothesized that metabolites involved in serotoninergic turnover in BD could influence DTI measures of WM microstructure. Peripheral levels of tryptophan, kynurenine, kynurenic acid, 3-hydroxy-kynurenine, and 5-HIAA were analysed in 22 patients affected by BD and 15 healthy controls. WM microstructure was evaluated using diffusion tensor imaging and tract-based spatial statistics with threshold-free cluster enhancement only in bipolar patients. We observed that kynurenic acid and 5-HIAA were reduced in BD and associated with DTI measures of WM integrity in several association fibres: inferior and superior longitudinal fasciculus, cingulum bundle, corpus callosum, uncus, anterior thalamic radiation and corona radiata. Our results seem to suggest that higher levels of 5-HIAA, a measure of serotonin levels, and higher levels of kynurenic acid, which protects from glutamate excitotoxicity, could exert a protective effect on WM microstructure. Reduced levels of these metabolites in BD thus seem to confirm a crucial role of serotonin turnover in BD pathophysiology.

The role of the kynurenine pathway of tryptophan metabolism in cardiovascular disease

Coronary heart disease and stroke, the deadliest forms of cardiovascular disease (CVD), are mainly caused by atherosclerosis, a chronic inflammatory disease of the artery wall driven by maladaptive immune responses in the vessel wall. Various risk factors for CVD influence this pathogenic process, including diabetes mellitus, hypertension, dyslipidaemia, and obesity. Indoleamine 2,3-dioxygenase (IDO), an enzyme catalyzing the rate-limiting step in the kynurenine pathway of tryptophan degradation, is strongly induced by inflammation in several tissues, including the artery wall. An increasing body of evidence indicates that IDO promotes immune tolerance, decreases inflammation, and functions as a homeostatic mechanism against excessive immune reactions.

This review provides an overview of the emerging field of the kynurenine pathway of tryptophan degradation in CVD, emphasizing the role of IDO-mediated tryptophan metabolism and its metabolites in the modulation of ‘classical’ cardiovascular risk factors, such as hypertension, obesity, lipid metabolism, diabetes mellitus, and in the development of atherosclerotic CVD.

Potential role of indoleamine 2,3-dioxygenase in primary biliary cirrhosis

Indoleamine 2,3-dioxygenase (IDO)-induced immunosuppression can be clinically beneficial for autoimmune diseases. Primary biliary cirrhosis (PBC) is characterized by autoimmune lesions of intrahepatic bile duct epithelial cells that may lead to irreversible cirrhosis or hepatocellular carcinoma. The present study assessed the expression and function of IDO in a cell culture model and in PBC patients. IDO expression was monitored in a human immortalized but non-malignant biliary epithelial cell (iBEC) line. Increased expression of IDO1/2 was observed in the iBECs following stimulation with interferon-γ (IFN-γ). The induction of IDO was IFN-γ-dependent, but was independent of the transforming growth factor-β (TGF-β) pathway. IDO enzymatic activity was observed in the supernatant of iBECs following stimulation with IFN-γ using colorimetric assays. A total of 47 serum samples from PBC patients were used to examine IDO activity by high-performance liquid chromatography, with samples from 24 healthy volunteers used as controls. Patients with PBC exhibited an increased rate of tryptophan to kynurenine conversion (P>0.01). Liver sections from patients with PBC (n=5) and those of healthy controls (n=5) were used for immunohistochemical studies. IDO expression was observed in biliary epithelial cells and in hepatocytes of PBC patients. Finally, the effect of tryptophan metabolites on human cluster of differentiation (CD) 4+ T cells in inducing polarization towards a regulatory T cell phenotype was examined. 3-Hydroxykynurenine significantly upregulated the fraction of CD4+ cells expressing forkhead box p3 (Foxp3). The results of the present study suggest a therapeutic opportunity for the management of PBC and indicate that tryptophan catabolism could serve as a potential biomarker to monitor disease progression.

The interplay between cytokines and the Kynurenine pathway in inflammation and atherosclerosis

The kynurenine pathway (KP) is the major metabolic route of tryptophan (Trp) metabolism. Indoleamine 2,3-dioxygenase (IDO1), the enzyme responsible for the first and rate-limiting step in the pathway, as well as other enzymes in the pathway, have been shown to be highly regulated by cytokines. Hence, the KP has been implicated in several pathologic conditions, including infectious diseases, psychiatric disorders, malignancies, and autoimmune and chronic inflammatory diseases. Additionally, recent studies have linked the KP with atherosclerosis, suggesting that Trp metabolism could play an essential role in the maintenance of immune homeostasis in the vascular wall. This review summarizes experimental and clinical evidence of the interplay between cytokines and the KP and the potential role of the KP in cardiovascular diseases.

Abnormal kynurenine pathway of tryptophan catabolism in cardiovascular diseases

Kynurenine pathway (KP) is the primary path of tryptophan (Trp) catabolism in most mammalian cells. The KP generates several bioactive catabolites, such as kynurenine (Kyn), kynurenic acid (KA), 3-hydroxykynurenine (3-HK), xanthurenic acid (XA), and 3-hydroxyanthranilic acid (3-HAA). Increased catabolite concentrations in serum are associated with several cardiovascular diseases (CVD), including heart disease, atherosclerosis, and endothelial dysfunction, as well as their risk factors, including hypertension, diabetes, obesity, and aging. The first catabolic step in KP is primarily controlled by indoleamine 2,3-dioxygenase (IDO) and tryptophan 2,3-dioxygenase (TDO). Following this first step, the KP has two major branches, one branch is mediated by kynurenine 3-monooxygenase (KMO) and kynureninase (KYNU) and is responsible for the formation of 3-HK, 3-HAA, and quinolinic acid (QA); and another branch is controlled by kynurenine amino-transferase (KAT), which generates KA. Uncontrolled Trp catabolism has been demonstrated in distinct CVD, thus, understanding the underlying mechanisms by which regulates KP enzyme expression and activity is paramount. This review highlights the recent advances on the effect of KP enzyme expression and activity in different tissues on the pathological mechanisms of specific CVD, KP is an inflammatory sensor and modulator in the cardiovascular system, and KP catabolites act as the potential biomarkers for CVD initiation and progression. Moreover, the biochemical features of critical KP enzymes and principles of enzyme inhibitor development are briefly summarized, as well as the therapeutic potential of KP enzyme inhibitors against CVD is briefly discussed.

PEG-rIL-10 treatment decreases FoxP3(+) Tregs despite upregulation of intratumoral IDO

IL-10 has been classically defined as a broad-spectrum immunosuppressant and is thought to facilitate the development of regulatory CD4(+) T cells. IL-10 is believed to represent one of the major suppressive factors secreted by IDO(+)FoxP3(+)CD4(+) Tregs. Contrary to this view, we have previously reported that PEGylated recombinant IL-10 (PEG-rIL-10) treatment of mice induces potent IFNγ and CD8(+) T-cell-dependent antitumor immunity. This hypothesis is currently being tested in clinical trials and we have reported that treatment of cancer patients with PEG-rHuIL-10 results in inhibition and regression of tumor growth as well as increased serum IFNγ. We have continued to assess PEG-rIL-10's pleiotropic effects and report that treatment of tumor-bearing mice and humans with PEG-rIL-10 increases intratumoral indoleamine 2, 3-dioxygenase (IDO) in an IFNγ-dependent manner. This should result in an increase in Tregs, but paradoxically our data illustrate that PEG-rIL-10 treatment of mice reduces intratumoral FoxP3(+)CD4(+) T cells in an IDO-independent manner. Additional investigation indicates that PEG-rIL-10 inhibits TGFβ/IL-2-dependent in vitro polarization of FoxP3(+)CD4(+) Tregs and potentiates IFNγ(+)T-bet(+)CD4(+) T cells. These data suggest that rather than acting as an immunosuppressant, PEG-rIL-10 may counteract the FoxP3(+)CD4(+) Treg suppressive milieu in tumor-bearing mice and humans, thereby further facilitating PEG-rIL-10's potent antitumor immunity.

Tryptophan-kynurenine pathway is dysregulated in inflammation, and immune activation

The kynurenine (Kyn) pathway is the major route for tryptophan (Trp) metabolism, and it contributes to several fundamental biological processes. Trp is constitutively oxidized by tryptophan 2, 3-dioxygenase in liver cells. In other cell types, it is catalyzed by an alternative inducible indoleamine-pyrrole 2, 3-dioxygenase (IDO) under certain pathophysiological conditions, which consequently increases the formation of Kyn metabolites. IDO is up-regulated in response to inflammatory conditions as a novel marker of immune activation in early atherosclerosis. Besides, IDO and the IDO-related pathway are important mediators of the immunoinflammatory responses in advanced atherosclerosis. In particular, Kyn, 3-hydroxykynurenine, and quinolinic acid are positively associated with inflammation, oxidative stress (SOX), endothelial dysfunction, and carotid artery intima-media thickness values in end-stage renal disease patients. Moreover, IDO is a potential novel contributor to vessel relaxation and metabolism in systemic infections, which is also activated in acute severe heart attacks. The Kyn pathway plays a key role in the increased prevalence of cardiovascular disease by regulating inflammation, SOX, and immune activation.

Inhibition of indoleamine 2,3-dioxygenase promotes vascular inflammation and increases atherosclerosis in Apoe-/- mice

AIMS

Atherosclerosis is a chronic inflammatory disease that is initiated by the retention and accumulation of low-density lipoprotein in the artery, leading to maladaptive response of cells from the immune system and vessel wall. Strong evidence implicates indoleamine 2,3-dioxygenase (IDO), the first and rate-limiting enzyme of the kynurenine pathway of tryptophan (Trp) degradation, with immune regulation and anti-inflammatory mechanisms in different diseases. However, the role of IDO and the endogenous degradation of Trp have never been directly examined in atherosclerosis development. We used the IDO inhibitor 1-methyl-Trp (1-MT) to determine the role of IDO-mediated Trp metabolism in vascular inflammation and atherosclerosis.

METHODS AND RESULTS

Apoe(-/-) mice were treated with 1-MT in drinking water for 8 weeks. Systemic IDO inhibition led to a significant increase in atherosclerotic lesions that were ∼58 and 54% larger in the aortic arch and root, respectively. 1-MT treatment enhanced vascular inflammation, up-regulated VCAM-1 and CCL2, and increased CD68 macrophage accumulation into the plaque. Notably, the rise in VCAM-1 expression was not limited to the plaque but also found in smooth muscle cells (SMCs) of the tunica media. Furthermore, we found that IDO-dependent Trp metabolism by SMCs regulates VCAM-1 expression, and that 1-MT-induced acceleration of atherosclerosis and vascular inflammation can be reversed by exogenous administration of the Trp metabolite 3-hydroxyanthranilic acid (3-HAA).

CONCLUSION

IDO-mediated Trp metabolism regulates vascular inflammation and plaque formation in hypercholesterolaemic Apoe(-/-) mice. Our data establish that this pathway plays a major role in the pathological process of atherogenesis.

Mycobacterium bovis BCG killed by extended freeze-drying induces an immunoregulatory profile and protects against atherosclerosis

OBJECTIVES

Atherosclerosis is an inflammatory disease of the arterial wall that leads to myocardial infarction and stroke. Regulatory T cells (Tregs) and IL-10 exert significant anti-atherogenic effects in experimental models of atherosclerosis by modulating vascular inflammation. We have previously shown that Mycobacterium bovis BCG killed by extended freeze-drying (EFD BCG) decreases lung and colon inflammation by recruiting IL-10-producing Tregs. Therefore, the aim of this study was to investigate the effect of EFD BCG on the development of atherosclerosis.

DESIGN

We used two strains of atherosclerosis-prone mice: Ldlr(-/-) (four or six EFD BCG injections) and Apoe(-/-) (six injections).

RESULTS

In both models, EFD BCG significantly reduced the size of atherosclerotic lesions, increased IL-10 production and reduced the serum levels of pro-inflammatory cytokines (IL-6, IL-13, KC and tumour necrosis factor-α). Shortly after treatment with EFD BCG, the number of plasmacytoid dendritic cells (pDCs) and Foxp3(+) Tregs in the draining lymph nodes increased. EFD BCG also led to accumulation of Tregs, but not of pDCs in the spleen, and reduced activity of NF-κB and increased activity of PPAR-γ in both the spleen and vascular tissue of treated mice.

CONCLUSION

EFD BCG has atheroprotective effects through IL-10 production and Treg expansion. These findings support a novel approach to the prevention and treatment of atherosclerosis.

Activation of NAD(P)H oxidase by tryptophan-derived 3-hydroxykynurenine accelerates endothelial apoptosis and dysfunction in vivo

RATIONALE

The kynurenine (Kyn) pathway is the major route for tryptophan (Trp) metabolism in mammals. The Trp-Kyn pathway is reported to regulate several fundamental biological processes, including cell death.

OBJECTIVE

The aim of this study was to elucidate the contributions and molecular mechanism of Trp-Kyn pathway to endothelial cell death.

METHODS AND RESULTS

Endogenous reactive oxygen species, endothelial cell apoptosis, and endothelium-dependent and endothelium-independent vasorelaxation were measured in aortas of wild-type mice or mice deficient for nicotinamide adenine dinucleotide phosphate [NAD(P)H] oxidase subunits (p47(phox) or gp91(phox)) or indoleamine-pyrrole 2,3-dioxygenase 1 with or without angiotensin (Ang) II infusion. As expected, AngII increased plasma levels of Kyn- and 3-hydroxykynurenine-modified proteins in endothelial cells in vivo. Consistent with this, AngII markedly increased the expression of indoleamine-pyrrole 2,3-dioxygenase in parallel with increased expression of interferon-γ. Furthermore, in wild-type mice, AngII significantly increased oxidative stress, endothelial cell apoptosis, and endothelial dysfunction. These effects of AngII infusion were significantly suppressed in mice deficient for p47(phox), gp91(phox), or indoleamine-pyrrole 2,3-dioxygenase 1, suggesting that AngII-induced enhancement of Kynurenines via NAD(P)H oxidase-derived oxidants causes endothelial cell apoptosis and dysfunction in vivo. Furthermore, interferon-γ neutralization eliminates AngII-increased superoxide products and endothelial apoptosis by inhibiting AngII-induced Kynurenines generation, suggesting that AngII-activated Kyn pathway is interferon-γ-dependent. Mechanistically, we found that AngII-enhanced 3-hydroxykynurenine promoted the generation of NAD(P)H oxidase-mediated superoxide anions by increasing the translocation and membrane assembly of NAD(P)H oxidase subunits in endothelial cells, resulting in accelerated apoptosis and consequent endothelial dysfunction.

CONCLUSIONS

Kyn pathway activation accelerates apoptosis and dysfunction of the endothelium by upregulating NAD(P)H-derived superoxide.

Nrf2 participates in depressive disorders through an anti-inflammatory mechanism

A causative relationship between inflammation and depression is gradually gaining consistency. Because Nrf2 participates in inflammation, we hypothesized that Nrf2 could play a role in depressive disorders. In this study, we have observed that Nrf2 deletion in mice results in: (i) a depressive-like behavior evaluated as an increase in the immobility time in the tail-suspension test and by a decrease in the grooming time in the splash test, (ii) reduced levels of dopamine and serotonin and increased levels of glutamate in the prefrontal cortex, (iii) altered levels of proteins associated to depression such as VEGF and synaptophysin and (iv) microgliosis. Furthermore, treatment of Nrf2 knockout mice with the anti-inflammatory drug rofecoxib reversed their depressive-like behavior, while induction of Nrf2 by sulforaphane, in an inflammatory model of depression elicited by LPS, afforded antidepressant-like effects. In conclusion, our results indicate that chronic inflammation due to a deletion of Nrf2 can lead to a depressive-like phenotype while induction of Nrf2 could become a new and interesting target to develop novel antidepressive drugs.

Immune effector mechanisms implicated in atherosclerosis: from mice to humans

According to the traditional view, atherosclerosis results from a passive buildup of cholesterol in the artery wall. Yet, burgeoning evidence implicates inflammation and immune effector mechanisms in the pathogenesis of this disease. Both innate and adaptive immunity operate during atherogenesis and link many traditional risk factors to altered arterial functions. Inflammatory pathways have become targets in the quest for novel preventive and therapeutic strategies against cardiovascular disease, a growing contributor to morbidity and mortality worldwide. Here we review current experimental and clinical knowledge of the pathogenesis of atherosclerosis through an immunological lens and how host defense mechanisms essential for survival of the species actually contribute to this chronic disease but also present new opportunities for its mitigation.

A dialogue between the immune system and brain, spoken in the language of serotonin

Neuropsychiatric disorders have long been linked to both immune system activation and alterations in serotonin (5-HT) signaling. In the CNS, the contributions of 5-HT modulate a broad range of targets, most notably, hypothalamic, limbic and cortical circuits linked to the control of mood and mood disorders. In the periphery, many are aware of the production and actions of 5-HT in the gut but are unaware that the molecule and its receptors are also present in the immune system where evidence suggests they contribute to the both innate and adaptive responses. In addition, there is clear evidence that the immune system communicates to the brain via both humoral and neuronal mechanisms, and that CNS 5-HT neurons are a direct or indirect target for these actions. Following a brief primer on the immune system, we describe our current understanding of the synthesis, release, and actions of 5-HT in modulating immune function, including the expression of 5-HT biosynthetic enzymes, receptors, and transporters that are typically studied with respect to the roles in the CNS. We then orient our presentation to recent findings that pro-inflammatory cytokines can modulate CNS 5-HT signaling, leading to a conceptualization that among the many roles of 5-HT in the body is an integrated physiological and behavioral response to inflammatory events and pathogens. From this perspective, altered 5-HT/immune conversations are likely to contribute to risk for neurobehavioral disorders historically linked to compromised 5-HT function or ameliorated by 5-HT targeted medications, including depression and anxiety disorders, obsessive-compulsive disorder (OCD), and autism. Our review raises the question as to whether genetic variation impacting 5-HT signaling genes may contribute to maladaptive behavior as much through perturbed immune system modulation as through altered brain mechanisms. Conversely, targeting the immune system for therapeutic development may provide an important opportunity to treat mental illness.

The genetics of selective serotonin reuptake inhibitors

Selective serotonin reuptake inhibitors (SSRIs) are among the most widely prescribed drugs in psychiatry. Based on the fact that SSRIs increase extracellular monoamine levels in the brain, the monoamine hypothesis of depression was introduced, postulating that depression is associated with too low serotonin, dopamine and noradrenaline levels. However, several lines of evidence indicate that this hypothesis is too simplistic and that depression and the efficacy of SSRIs are dependent on neuroplastic changes mediated by changes in gene expression. Because a coherent view on global gene expression is lacking, we aim to provide an overview of the effects of SSRI treatment on the final targets of 5-HT receptor signal transduction pathways, namely the transcriptional regulation of genes. We address gene polymorphisms in humans that affect SSRI efficacy, as well as in vitro studies employing human-derived cells. We also discuss the molecular targets affected by SSRIs in animal models, both in vivo and in vitro. We conclude that serotonin transporter gene variation in humans affects the efficacy and side-effects of SSRIs, whereas SSRIs generally do not affect serotonin transporter gene expression in animals. Instead, SSRIs alter mRNA levels of genes encoding serotonin receptors, components of non-serotonergic neurotransmitter systems, neurotrophic factors, hypothalamic hormones and inflammatory factors. So far little is known about the epigenetic and age-dependent molecular effects of SSRIs, which might give more insights in the working mechanism(s) of SSRIs.

The role of zinc in neurodegenerative inflammatory pathways in depression

According to new hypothesis, depression is characterized by decreased neurogenesis and enhanced neurodegeneration which, in part, may be caused by inflammatory processes. There is much evidence indicating that depression, age-related changes often associated with impaired brain function and cognitive performances or neurodegenerative processes could be related to dysfunctions affecting the zinc ion availability. Clinical studies revealed that depression is accompanied by serum hypozincemia, which can be normalized by successful antidepressant treatment. In patients with major depression, a low zinc serum level was correlated with an increase in the activation of markers of the immune system, suggesting that this effect may result in part from a depression-related alteration in the immune-inflammatory system. Moreover, a preliminary clinical study demonstrated the benefit of zinc supplementation in antidepressant therapy in both treatment non-resistant and resistant patients. In the preclinical study, the antidepressant activity of zinc was observed in the majority of rodent tests and models of depression and revealed a causative role for zinc deficiency in the induction of depressive-like symptoms, the reduction of neurogenesis and neuronal survival or impaired learning and memory ability. This paper provides an overview of the clinical and experimental evidence that implicates the role of zinc in the pathophysiology and therapy of depression within the context of the inflammatory and neurodegenerative hypothesis of this disease.

Manipulation of indoleamine 2,3 dioxygenase; a novel therapeutic target for treatment of diseases

BACKGROUND

The discovery of indoleamine 2,3-dioxygenase (IDO) as a modulator for the maintenance of fetomaternal immuno-privileged state has been heralded as a significant step in further defining the role of IDO in immunobiology. IDO is an IFN-inducible, intracellular enzyme that catalyzes the initial and rate-limiting step in the degradation of the essential amino acid, tryptophan. It has been suggested that IDO has the capacity to regulate the immune system via two discrete mechanisms; firstly the deprivation of tryptophan, which is essential for T cell proliferation and via the cytotoxic effects of tryptophan metabolites on T(H)1 cell survival.

METHODS

The sources of information used to prepare the paper are published work on Pubmed/Medline. In this review, we examine the therapeutic role of modulating IDO activity a variety of disease states including tumour tolerance, chronic infection, transplant rejection, autoimmunity and asthma. We propose that IDO represents a novel therapeutic target for the treatment of these diseases. We also explore the diverse strategies which are being employed, either to augment or to inhibit IDO activity in order to modify various disease processes. The limitations associated with these strategies are also scrutinized.

A functional serotonin transporter gene polymorphism and depressive effects associated with interferon-alpha treatment

BACKGROUND

Interferon-alpha (IFN-alpha) treatment frequently induces depression, potentially leading to early dose reductions or a shorter duration of treatment, which can adversely affect outcomes, including quality of life.

OBJECTIVE

Defining relevant risk factors for IFN-alpha-induced depression is essential in order to identify prophylactic treatment strategies.

METHOD

The authors examined whether a functional polymorphism (5-HTTLPR) in the gene encoding the serotonin transporter moderates IFN-alpha-induced depressive symptoms in 1,015 patients with chronic hepatitis C (CHC) receiving pegylated IFN-alpha and ribavirin. Depressive symptoms were assessed at baseline, 12 weeks, and 20 weeks of treatment.

RESULTS

Depression symptoms increased during antiviral treatment; 5-HTTLPR genotype moderated IFN-alpha-induced depression symptoms in both non-Hispanic Caucasians and Hispanic patients, although the opposite risk allele was associated with depression in the two populations.

CONCLUSION

5-HTTLPR may moderate risk for the development of depressive symptoms during IFN-alpha therapy for CHC in a population-specific manner.

Kynurenine is an endothelium-derived relaxing factor produced during inflammation

Control of blood vessel tone is central to vascular homeostasis. Here we show that metabolism of tryptophan to kynurenine by indoleamine 2,3-dioxygenase (Ido) expressed in endothelial cells contributes to arterial vessel relaxation and the control of blood pressure. Infection of mice with malarial parasites (Plasmodium berghei) or induction of endotoxemia in mice led to endothelial expression of Ido, decreased plasma tryptophan concentration, increased kynurenine concentration and hypotension. Pharmacological inhibition of Ido increased blood pressure in systemically inflamed mice but not in mice deficient in Ido or interferon-gamma, which is required for Ido induction. Both tryptophan and kynurenine dilated preconstricted porcine coronary arteries; the dilating effect of tryptophan required the presence of active Ido and an intact endothelium, whereas the effect of kynurenine was endothelium independent. The arterial relaxation induced by kynurenine was mediated by activation of the adenylate and soluble guanylate cyclase pathways. Kynurenine administration decreased blood pressure in a dose-dependent manner in spontaneously hypertensive rats. Our results identify tryptophan metabolism by Ido as a new pathway contributing to the regulation of vascular tone.

Schizophrenia: from the brain to peripheral markers. A consensus paper of the WFSBP task force on biological markers

Objective. The phenotypic complexity, together with the multifarious nature of the so-called "schizophrenic psychoses", limits our ability to form a simple and logical biologically based hypothesis for the disease group. Biological markers are defined as biochemical, physiological or anatomical traits that are specific to particular conditions. An important aim of biomarker discovery is the detection of disease correlates that can be used as diagnostic tools. Method. A selective review of the WFSBP Task Force on Biological Markers in schizophrenia is provided from the central nervous system to phenotypes, functional brain systems, chromosomal loci with potential genetic markers to the peripheral systems. Results. A number of biological measures have been proposed to be correlated with schizophrenia. At present, not a single biological trait in schizophrenia is available which achieves sufficient specificity, selectivity and is based on causal pathology and predictive validity to be recommended as diagnostic marker. Conclusions. With the emergence of new technologies and rigorous phenotypic subclassification the identification of genetic bases and assessment of dynamic disease related alterations will hopefully come to a new stage in the complex field of psychiatric research.

[Chlamydophila pneumoniae: from its proteomics to arteriosclerosis]

Chlamydophila pneumoniae is a highly prevalent intracellular human pathogen with a unique biphasic life cycle. It is a common cause of upper respiratory infection and pneumonia, and is currently being studied as a potential risk factor for the development of atherosclerotic cardiovascular disease. The outer membrane surface antigens of C. pneumoniae are highly complex: some, such as the major outer membrane protein, are specific, but poorly immunodominant, whereas others have stronger immunogenicity, but are cross-reactive among Chlamydia species. Therefore, new, highly immunodominant, species-specific antigens should be sought. In this regard, the polymorphic membrane proteins (PMPs) are a) unique to Chlamydiae, b) often exposed on the surface of the bacteria, and c) highly immunogenic; these factors make them potential candidates for application in laboratory assays. Other chlamydial antigens, such as heat shock protein (HSP) 60, have been associated with atherosclerotic lesions because of their ability to induce an immunological attack on the endothelial wall. Over the last decade, several studies have suggested a potential role of chronic C. pneumoniae infection in human atherosclerosis. Nevertheless, prospective studies with sufficiently large samples and a healthy comparison group, using a combination of direct and indirect microbiological techniques in the same subject and sample, are needed to establish a relationship between the infection and disease activity.

Manipulation of indoleamine 2,3-dioxygenase (IDO) for clinical transplantation: promises and challenges

BACKGROUND

Since the discovery that indoleamine 2,3-dioxygenase (IDO) is a modulator for maintenance of fetomaternal immuno-privilege state, it has been implicated in tumour tolerance, autoimmune diseases and asthma. IDO is an IFN-gamma-inducible, intracellular enzyme that catalyzes the initial and rate-limiting step in the degradation of tryptophan. It has been suggested that IDO can regulate the immune system either through deprivation of tryptophan that is essential for T cell proliferation or via cytotoxic effects of kynurenine pathway metabolites on T cell survival.

METHODS

The sources of information used were obtained through Pubmed/Medline.

RESULTS/CONCLUSION

While IDO emerges as a regulator of immunity, its role in controlling allo-response is unfolding. IDO can control T cell responses to allo-antigens and induce generation of allo-specific regulatory T cells. Exploiting IDO as a modulator of transplant rejection, many groups have manipulated its activity to prolong allograft survival in transplantation models. Despite the initial promise, its application to clinical transplantation may be limited. We therefore examine the potentials and limitations associated with clinical translation of IDO into a therapeutic.

Mouse pancreatic islets are resistant to indoleamine 2,3 dioxygenase-induced general control nonderepressible-2 kinase stress pathway and maintain normal viability and function

Islet transplantation is a promising treatment for diabetes. However, it faces several challenges including requirement of systemic immunosuppression. Indoleamine 2,3-dioxygenase (IDO), a tryptophan degrading enzyme, is a potent immunomodulatory factor. Local expression of IDO in bystander fibroblasts suppresses islet allogeneic immune response in vitro. The aim of the present study was to investigate the impact of IDO on viability and function of mouse islets embedded within IDO-expressing fibroblast-populated collagen scaffold. Mouse islets were embedded within collagen matrix populated with IDO adenovector-transduced or control fibroblasts. Proliferation, insulin content, glucose responsiveness, and activation of general control nonderepressible-2 kinase stress-responsive pathway were then measured in IDO-exposed islets. In vivo viabilities of composite islet grafts were also tested in a syngeneic diabetic animal model. No reduction in islet cells proliferation was detected in both IDO-expressing and control composites compared to the baseline rates. Islet functional studies showed normal insulin content and secretion in both preparations. In contrast to lymphocytes, general control nonderepressible-2 kinase pathway was not activated in islets cocultured with IDO-expressing fibroblasts. When transplanted to diabetic mice, syngeneic IDO-expressing composite islet grafts were functional up to 100 days tested. These findings collectively confirm normal viability and functionality of islets cocultured with IDO-expressing cells and indicate the feasibility of development of a functional nonrejectable islet graft.

Interferon-alpha-induced serotonin uptake in Jurkat T cells via mitogen-activated protein kinase and transcriptional regulation of the serotonin transporter

Interferon (IFN)-alpha upregulates serotonin (5-HT) uptake and serotonin transporter (5-HTT) messenger ribonucleic acid (mRNA) expression in immune cells, which implies the mechanism underlying IFN-alpha-induced depression. However, the signal transduction of this effect remains unclear. We investigated whether the effects of IFN-alpha on the functions of 5-HTT were related to mitogen-activated protein kinase (MAPK). By performing Western blotting, real-time reverse transcriptase-polymerase chain reaction and [3H]5-HT labelling, we examined MAPK phosphorylation, 5-HTT mRNA expression and 5-HT uptake in Jurkat T cells. The cells had been cultured for different time periods (1) with IFN-alpha alone and (2) preincubated with either MAPK inhibitors or with the selective serotonin reuptake inhibitor, fluoxetine, and subsequently cultured along with IFN-alpha. The levels of MAPK phosphorylation, 5-HTT mRNA expression and 5-HT uptake all increased in the IFN-alpha-treated cells but were blocked in those that were pretreated with MAPK inhibitors and fluoxetine. These results appear to clarify the association of depression with IFN-alpha-induced 5-HT uptake that reduces the 5-HT levels and IFN-alpha-regulated transcription of 5-HTT; further, the results suggest the involvement of MAPK in this process.

Induction of Indoleamine 2,3-Dioxygenase in Vascular Smooth Muscle Cells by Interferon-γ Contributes to Medial Immunoprivilege

Atherosclerosis and graft arteriosclerosis are characterized by leukocytic infiltration of the vessel wall that spares the media. The mechanism(s) for medial immunoprivilege is unknown. In a chimeric humanized mouse model of allograft rejection, medial immunoprivilege was associated with expression of IDO by vascular smooth muscle cells (VSMCs) of rejecting human coronary artery grafts. Inhibition of IDO by 1-methyl-tryptophan (1-MT) increased medial infiltration by allogeneic T cells and increased VSMC loss. IFN-gamma-induced IDO expression and activity in cultured human VSMCs was considerably greater than in endothelial cells (ECs) or T cells. IFN-gamma-treated VSMCs, but not untreated VSMCs nor ECs with or without IFN-gamma pretreatment, inhibited memory Th cell alloresponses across a semipermeable membrane in vitro. This effect was reversed by 1-MT treatment or tryptophan supplementation and replicated by the absence of tryptophan, but not by addition of tryptophan metabolites. However, IFN-gamma-treated VSMCs did not activate allogeneic memory Th cells, even after addition of 1-MT or tryptophan. Our work extends the concept of medial immunoprivilege to include immune regulation, establishes the compartmentalization of immune responses within the vessel wall due to distinct microenvironments, and demonstrates a duality of stimulatory EC signals versus inhibitory VSMC signals to artery-infiltrating T cells that may contribute to the chronicity of arteriosclerotic diseases.

Cytokines and serotonin transporter in patients with major depression

Altered cytokine secretion as a mechanism in the etiology of depression is still obscure. The serotonin transporter (5-HTT) may play an important role in the termination of serotonergic neurotransmission by serotonin (5-HT) uptaking into presynaptic neurons and representing as an initial action site for selective 5-HTT reuptake inhibitors (SSRI). In our study, we evaluated whether cytokines and 5-HTT acted as biological markers for depression. Blood samples were collected from 42 participants. The differences in cytokine and 5-HTT mRNA expressions of leukocytes were assessed between the patients with major depression (n=20) and the healthy controls (n=22), along with the measurements prior and after treatment with a SSRI, fluoxetine, for 3 months in the follow-up patient group (n=8). The results revealed that the mRNA expressions of IL-1beta, IL-6, IFNgamma, TNFalpha, and 5-HTT were higher in the depressed patients than those of the healthy controls. The higher level of mRNA expressions of IFNgamma and 5-HTT diminished after fluoxetine treatment. Furthermore, we found a positive correlation between 5-HTT and cytokines mRNA expressions in total participants, which suggested that pro-inflammatory cytokines and 5-HTT might play critical roles in the pathogenesis of major depression and that their levels were affected by chronic treatment with 5-HTT inhibitors.

Serotonin transporter mRNA expression is decreased by lamivudine and ribavirin and increased by interferon in immune cells

Clinical reports document that depression as a side effect is more prevalent in hepatic patients given interferon (IFN)-alpha therapy than in those given lamivudine. The mechanisms, however, are poorly understood. Serotonin transporter (5-HTT), via uptake of serotonin (5-HT) into presynaptic serotoninergic neurons, is an initial action site for antidepressants. Real-time polymerase chain reaction (PCR) was used to quantify 5-HTT mRNA expression in immune cells in order to evaluate whether 5-HTT acted as an indicator of depression. Results showed that the 5-HTT mRNA expression was much higher in T-cell and B-cell lines than that in a monocytic cell line. Treatment with either lamivudine or ribavirin reduced the 5-HTT mRNA expression, protein level and 5-HT uptake in T-cell line. Treatment with IFN-alpha, however, increased those levels in the same group. A similar effect was observed in peripheral blood mononuclear cells (PBMC). Mimicking clinical use by treating PBMC with a combination of IFN-alpha and ribavirin increased the 5-HTT mRNA expression level. Our study indicates that these therapeutic drugs regulate 5-HTT expression, which implies that 5-HTT might be a trait marker in IFN-alpha-induced depression after hepatic therapy.

Cytokine-serotonin interaction through IDO: a neurodegeneration hypothesis of depression

There are different theories and hypotheses related to the aetiology of depression. The interaction between brain 5-HT level and the activity of its autoreceptors plays a role in mood changes and depression. In major depression, activation of the inflammatory response system (IRS) and, increased concentrations of proinflammatory cytokines, prostaglandin E2 and negative immuno-regulatory cytokines in peripheral blood have been reported. Recently, pro-inflammatory cytokines have been found to have profound effects on the metabolism of brain serotonin through the enzyme indoleamine-2,3-dioxygenase (IDO) that metabolizes the tryptophan, the precursor of 5-HT to neurodegenerative quinolinate and neuroprotective kynurenate. The cytokine-serotonin interaction that leads to the challenge between quinolinate and kynurenate in the brain explains the neurodegeneration hypothesis of depression.

The role of the cytokine network in psychological stress

Although a considerable amount of evidence has shown that psychological stress alters peripheral and brain cytokines, the physiological significance of cytokine alteration in psychological stress remains to be elucidated. The aims of this review are to analyze the influence of acute and chronic psychological stresses on the cytokine network in animals and in humans, and to explore the pathophysiological implication of the cytokine changes in psychological stress. Acute psychological stress may increase proinflammatory cytokines both in animals and in humans, and increase T-helper-1 cell cytokines in humans. Investigations into the effect of chronic psychological stress on cytokine production in animals gives mixed results. However, in humans, academic exam stress or care-giver's stress appears to induce a shift in the Th1/Th2 cytokine balance toward a Th2 response and increase proinflammatory cytokines. Psychological stress-induced cytokines stimulate the activity of indoleamine 2,3 dioxygenase (IDO) and could induce serotonin depletion-related disorders such as depression in susceptible individuals. Psychological stress-induced production of cytokines may increase the risk for human diseases, such as cardiovascular disease and exacerbation of autoimmune diseases. Proinflammatory cytokines may also play a regulatory role in glucocorticoid resistance and may be involved in wound healing and skin barrier function alterations. Finally, psychological stress-induced production of cytokines may play a role in neurodegenerative changes in the brain.