Systemic Markers of Interferon-γ–Mediated Immune Activation and Long-Term Prognosis in Patients With Stable Coronary Artery Disease

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.

The kynurenine:tryptophan ratio as a predictor of incident type 2 diabetes mellitus in individuals with coronary artery disease

AIMS/HYPOTHESIS

The tryptophan metabolite kynurenine has potent immune modulatory and vasoactive properties. Experimental data implicate kynurenine in obesity-related morbidities. Epidemiological studies are, however, sparse. We evaluated associations of the plasma and urine kynurenine:tryptophan ratio (KTR) to incident type 2 diabetes.

METHODS

We followed 2519 individuals with coronary artery disease (CAD; 73.1% men) without diabetes at baseline for a median of 7.6 years, during which 173 (6.9%) new incidences of type 2 diabetes were identified. Multivariate Cox regression analyses were applied to investigate the prospective relationships of plasma and urine KTR with new onset type 2 diabetes.

RESULTS

At inclusion, mean (SD) age was 61.3 (10.4) years, BMI was 25.9 (3.71) kg/m2 and median (interquartile range) HbA1c was 5.6% (5.0%-6.0%) (38 [31-42] mmol/mol). Plasma KTR was not significantly related to type 2 diabetes risk. By contrast, urine KTR showed a strong positive association. Comparing quartile 4 with quartile 1, the HRs (95% CIs) were 2.59 (1.56, 4.30) and 2.35 (1.39, 3.96) in the age- and sex-adjusted and multivariate models, respectively.

CONCLUSIONS/INTERPRETATION

Urine KTR is a strong predictor of incident type 2 diabetes in individuals with CAD. Potential clinical implications and possible pathogenic roles of renal kynurenine excretion in type 2 diabetes development should be further elucidated.

Immune biomarkers in older adults: Role of physical activity

Aging is associated with a decline in the normal functioning of the immune system. Several studies described the relationship between immunological alterations, including immunosenescence and inflammation, and aging or age-related outcomes, such as sarcopenia, depression, and neurodegenerative disorders. Physical activity is known to improve muscle function and to exert a number of benefits on older adult health, including reduced risk for heart and metabolic system chronic diseases. However, the positive influence of physical activity on the immune system has not been elucidated. In order to shed light on the role of physical activity in immune responses of older individuals, a number of immunological parameters comprising % lymphocyte subsets (CD3⁺, CD4⁺, CD8⁺, CD19⁺, and CD16⁺56⁺) and serum levels of neopterin and tryptophan metabolism products were evaluated in peripheral blood samples of older adults performing normal (N = 170) or reduced (N = 89) physical activity. In addition, the potential influence of other clinical and epidemiological factors was also considered. Results showed that subjects with reduced physical activity displayed significantly higher levels of CD4⁺/CD8⁺ ratio, kynurenine/tryptophan ratio, and serum neopterin, along with lower %CD19⁺ cells and tryptophan concentrations. Further, some immunological biomarkers were associated with cognitive impairment and functional status. These data contribute to reinforce the postulation that physical activity supports healthy aging, particularly by helping to protect the immunological system from aging-related changes.

The tryptophan/kynurenine pathway, systemic inflammation, and long-term outcome after kidney transplantation

Tryptophan is metabolized along the kynurenine pathway, initially to kynurenine, and subsequently to cytotoxic 3-hydroxykynurenine. There is increasing interest in this pathway because of its proinflammatory nature, and drugs interfering in it have received increasing attention. We aimed to investigate whether serum and urinary parameters of the tryptophan/kynurenine pathway, and particularly cytotoxic 3-hydroxykynurenine, are associated with systemic inflammation and long-term outcome in renal transplant recipients (RTR). Data were collected in outpatient RTR with a functioning graft for >1 yr. Tryptophan, kynurenine, and 3-hydroxykynurenine in serum and urine were measured using LC-MS/MS. A total of 561 RTR (age: 51 ± 12 yr; 56% male) were included at a median of 6.0 (2.6-11.6) yr posttransplantation. Baseline median serum tryptophan was 40.0 (34.5-46.0) µmol/l, serum kynurenine was 1.8 (1.4-2.2) µmol/l, and serum 3-hydroxykynurenine was 42.2 (31.0-61.7) nmol/l. Serum kynurenine and 3-hydroxykynurenine were strongly associated with parameters of systemic inflammation. During follow-up for 7.0 (6.2-7.5) yr, 51 RTR (9%) developed graft failure and 120 RTR (21%) died. Both serum kynurenine and 3-hydroxykynurenine were independently associated with graft failure [HR 1.72 (1.23-2.41), P = 0.002; and HR 2.03 (1.42-2.90), P < 0.001]. Serum 3-hydroxykynurenine was also independently associated with mortality [HR 1.37 (1.08-1.73), P = 0.01], whereas serum kynurenine was not. Urinary tryptophan/kynurenine pathway parameters were not associated with outcome. Of tryptophan metabolites, serum 3-hydroxykynurenine is cross-sectionally most strongly and consistently associated with systemic inflammation and prospectively with adverse long-term outcome after kidney transplantation. Serum 3-hydroxykynurenine may be an interesting biomarker and target for the evaluation of drugs interfering in the tryptophan/kynurenine pathway.

Crosstalk between Tryptophan Metabolism and Cardiovascular Disease, Mechanisms, and Therapeutic Implications

The cardiovascular diseases (CVD) associated with the highest rates of morbidity are coronary heart disease and stroke, and the primary etiological factor leading to these conditions is atherosclerosis. This long-lasting inflammatory disease, characterized by how it affects the artery wall, results from maladaptive immune responses linked to the vessel wall. Tryptophan (Trp) is oxidized in a constitutive manner by tryptophan 2,3-dioxygenase in liver cells, and for alternative cell types, it is catalyzed in the presence of a differently inducible indoleamine 2,3-dioxygenase (IDO1) in the context of a specific pathophysiological environment. Resultantly, this leads to a rise in the production of kynurenine (Kyn) metabolites. Inflammation in the preliminary stages of atherosclerosis has a significant impact on IDO1, and IDO1 and the IDO1-associated pathway constitute critical mediating agents associated with the immunoinflammatory responses that characterize advanced atherosclerosis. The purpose of this review is to survey the recent literature addressing the kynurenine pathway of tryptophan degradation in CVD, and the author will direct attention to the function performed by IDO1-mediated tryptophan metabolism.

The Kynurenine Pathway in the Acute and Chronic Phases of Cerebral Ischemia

Kynurenines are a wide range of catabolites which derive from tryptophan through the "Kynurenine Pathway" (KP). In addition to its peripheral role, increasing evidence shows a role of the KP in the central nervous system (CNS), mediating both physiological and pathological functions. Indeed, an imbalance in this route has been associated with several neurodegenerative disorders such as Alzheimer´s and Huntington´s diseases. Altered KP catabolism has also been described during both acute and chronic phases of stroke; however the contribution of the KP to the pathophysiology of acute ischemic damage and of post-stroke disorders during the chronic phase including depression and vascular dementia, and the exact mechanisms implicated in the regulation of the KP after stroke are not well established yet. A better understanding of the regulation and activity of the KP after stroke could provide new pharmacological tools in both acute and chronic phases of stroke. In this review, we will make an overview of CNS modulation by the KP. We will detail the KP contribution in the ischemic damage, how the unbalance of the KP might trigger an alteration of the cognitive function after stroke as well as potential targets for the development of new drugs.

Elevated Circulating Concentrations of Interferon-Gamma in Latent Tuberculosis Infection

BACKGROUND

Latent tuberculosis infection (LTBI) has been associated with increased immune activation. We assessed circulating concentrations of interferon-gamma in persons with LTBI.

METHODS

We used the 2011-2012 National Health Nutritional Examination Survey (NHANES) to identify adults with and without LTBI by QuantiFERON®-TB Gold In-Tube (QFT) results. Non-LTBI persons were 1:1 age-, gender-, and race-matched to LTBI persons using propensity scores. We compared the plasma concentrations of interferon-gamma measured from the unstimulated, negative control QFT tube between LTBI and non-LTBI persons. We used Mann-Whitney tests and ordered logistic regressions for comparisons.

RESULTS

There were 430 LTBI and 430 non-LTBI matched persons included in the analysis. LTBI was associated with higher circulating concentrations of interferon-gamma (median, 3 pg/mL; IQR, 2 - 5) compared to non-LTBI (median, 2.5 pg/mL; IQR, 1.5 - 3.5); P < 0.001. LTBI remained associated with higher interferon-gamma concentrations after adjusting for age, gender, race, diabetes, hypertension, tobacco use, HIV status, body mass index, lipid profile, and lymphocyte count (odds ratio, 1.79, 95% CI, 1.26 - 2.53). Results remained similar when tuberculin skin testing defined LTBI.

CONCLUSIONS

LTBI was associated with increased circulating interferon-gamma concentrations. Future studies are needed to further characterize immune activation in LTBI and its potential long-term consequences.

Vitamin B-6 catabolism and long-term mortality risk in patients with coronary artery disease

BACKGROUND

Low vitamin B-6 status has been related to increased risk of coronary artery disease (CAD), which is a condition that is associated with inflammation. The most common status marker, plasma pyridoxal 5'-phosphate (PLP), decreases during inflammation; therefore, causal relations are uncertain.

OBJECTIVE

We evaluated the vitamin B-6 biomarkers PLP, pyridoxal, and pyridoxic acid (PA) and the pyridoxic acid:(pyridoxal + PLP) ratio (PAr), a proposed marker of vitamin B-6 catabolism during activated cellular immunity, as predictors of mortality.

DESIGN

Associations with risks of long-term all-cause mortality and cardiovascular mortality were evaluated with the use of Cox regression in patients who were undergoing elective coronary angiography for suspected stable angina pectoris (SAP) (n = 4131) and an independent cohort of patients who were hospitalized for acute myocardial infarction (AMI) (n = 3665).

RESULTS

Plasma PLP (AMI patients only) and PA predicted all-cause mortality in models that were adjusted for established risk predictors, but associations were attenuated or nonsignificant after additional adjustment for inflammatory markers. PAr was correlated with biomarkers of inflammation (Pearson's r ≥ 0.37) and predicted all-cause mortality and cardiovascular mortality after adjustment for established risk predictors. In SAP patients, PAr had greater predictive strength than did current smoking, diabetes, hypertension, apolipoproteins, or C-reactive protein. PAr provided multiadjusted HRs per SD of 1.45 (95% CI: 1.30, 1.63) and 1.31 (95% CI: 1.21, 1.41) in SAP and AMI patients, respectively. In both cohorts, PAr was a particularly strong predictor of all-cause mortality for patients with no previous CAD history (P-interaction ≤ 0.04).

CONCLUSION

PAr may capture unique aspects of inflammatory activation and thus provide new insights into disease mechanisms that may aid in identifying patients at increased risk of future fatal events.

B vitamin treatments modify the risk of myocardial infarction associated with a MTHFD1 polymorphism in patients with stable angina pectoris

BACKGROUND

Methylenetetrahydrofolate dehydrogenase (MTHFD1) catalyzes three sequential reactions that metabolize derivatives of tetrahydrofolate (THF) in folate-dependent one-carbon metabolism. Impaired MTHFD1 flux has been linked to disturbed lipid metabolism and oxidative stress. However, limited information is available on its relation to the development of atherothrombotic cardiovascular disease.

METHODS AND RESULTS

We explored the association between a MTHFD1 polymorphism (rs1076991 C > T) and acute myocardial infarction (AMI), and potential effect modifications by folic acid/B12 and/or vitamin B6 treatment in suspected stable angina pectoris patients (n = 2381) participating in the randomized Western Norway B Vitamin Intervention Trial (WENBIT). During the median follow-up of 4.9 years 204 participants (8.6%) suffered an AMI. After adjusting for established CVD risk factors, the MTHFD1 polymorphism was significantly associated with AMI (HR: 1.49; 95% CI, 1.23-1.81). A similar association was observed among patients allocated to treatment with vitamin B6 alone (HR: 1.53; 95% CI, 1.01-2.31), and an even stronger relationship was seen in patients treated with both vitamin B6 and folic acid/B12 (HR: 2.35; 95% CI, 1.55-3.57). However, no risk association between the MTHFD1 polymorphism and AMI was seen in patients treated with placebo (HR: 1.29; 95% CI, 0.86-1.93) or folic acid/B12 (1.17; 95% CI, 0.83-1.65).

CONCLUSION

A common and functional MTHFD1 polymorphism is associated with increased risk of AMI, although the risk seems to be dependent on specific B vitamin treatment. Further studies are warranted to elucidate the possible mechanisms, also in order to explore potential effect modifications by nutritional factors.

A Novel Protective Function of 5-Methoxytryptophan in Vascular Injury

5-Methoxytryptophan (5-MTP), a 5-methoxyindole metabolite of tryptophan metabolism, was recently shown to suppress inflammatory mediator-induced cancer cell proliferation and migration. However, the role of 5-MTP in vascular disease is unknown. In this study, we investigated whether 5-MTP protects against vascular remodeling following arterial injury. Measurements of serum 5-MTP levels in healthy subjects and patients with coronary artery disease (CAD) showed that serum 5-MTP concentrations were inversely correlated with CAD. To test the role of 5-MTP in occlusive vascular disease, we subjected mice to a carotid artery ligation model of neointima formation and treated mice with vehicle or 5-MTP. Compared with vehicle-treated mice, 5-MTP significantly reduced intimal thickening by 40% 4 weeks after ligation. BrdU incorporation assays revealed that 5-MTP significantly reduced VSMC proliferation both in vivo and in vitro. Furthermore, 5-MTP reduced endothelial loss and detachment, ICAM-1 and VCAM-1 expressions, and inflammatory cell infiltration in the ligated arterial wall, suggesting attenuation of endothelial dysfunction. Signaling pathway analysis indicated that 5-MTP mediated its effects predominantly via suppressing p38 MAPK signaling in endothelial and VSMCs. Our data demonstrate a novel vascular protective function of 5-MTP against arterial injury-induced intimal hyperplasia. 5-MTP might be a therapeutic target for preventing and/or treating vascular remodeling.

Tryptophan Metabolism in Allergic Disorders

Allergic diseases such as asthma and rhinitis, as well the early phase of atopic dermatitis, are characterized by a Th2-skewed immune environment. Th2-type cytokines are upregulated in allergic inflammation, whereas there is downregulation of the Th1-type immune response and related cytokines, such as interferon-x03B3; (IFN-x03B3;). The latter is a strong inducer of indoleamine 2,3-dioxygenase-1 (IDO-1), which degrades the essential amino acid tryptophan, as part of an antiproliferative strategy of immunocompetent cells to halt the growth of infected and malignant cells, and also of T cells - an immunoregulatory intervention to avoid overactivation of the immune system. Raised serum tryptophan concentrations have been reported in patients with pollen allergy compared to healthy blood donors. Moreover, higher baseline tryptophan concentrations have been associated with a poor response to specific immunotherapy. It has been shown that the increase in tryptophan concentrations in patients with pollen allergy only exists outside the pollen season, and not during the season. Interestingly, there is only a minor alteration of the kynurenine to tryptophan ratio (Kyn/Trp, an index of tryptophan breakdown). The reason for the higher tryptophan concentrations in patients with pollen allergy outside the season remains a matter of discussion. To this regard, the specific interaction of nitric oxide (NO∙) with the tryptophan-degrading enzyme IDO-1 could be important, because an enhanced formation of NO∙ has been reported in patients with asthma and allergic rhinitis. Importantly, NO∙ suppresses the activity of the heme enzyme IDO-1, which could explain the higher tryptophan levels. Thus, inhibitors of inducible NO∙ synthase should be reconsidered as candidates for antiallergic therapy out of season that may abrogate the arrest of IDO-1 by decreasing the production of NO∙. Considering its association with the pathophysiology of atopic disease, tryptophan metabolism may play a relevant role in the pathophysiology of allergic disorders.

Plasma Biomarkers of Inflammation, the Kynurenine Pathway, and Risks of All-Cause, Cancer, and Cardiovascular Disease Mortality: The Hordaland Health Study

We aimed to evaluate 10 biomarkers related to inflammation and the kynurenine pathway, including neopterin, kynurenine:tryptophan ratio, C-reactive protein, tryptophan, and 6 kynurenines, as potential predictors of all-cause and cause-specific mortality in a general population sample. The study cohort was participants involved in a community-based Norwegian study, the Hordaland Health Study (HUSK). We used Cox proportional hazards models to assess associations of the biomarkers with all-cause mortality and competing-risk models for cause-specific mortality. Of the 7,015 participants, 1,496 deaths were recorded after a median follow-up time of 14 years (1998–2012). Plasma levels of inflammatory markers (neopterin, kynurenine:tryptophan ratio, and C-reactive protein), anthranilic acid, and 3-hydroxykynurenine were positively associated with all-cause mortality, and tryptophan and xanthurenic acid were inversely associated. Multivariate-adjusted hazard ratios for the highest (versus lowest) quartiles of the biomarkers were 1.19–1.60 for positive associations and 0.73–0.87 for negative associations. All of the inflammatory markers and most kynurenines, except kynurenic acid and 3-hydroxyanthranilic acid, were associated with cardiovascular disease (CVD) mortality. In this general population, plasma biomarkers of inflammation and kynurenines were associated with risk of all-cause, cancer, and CVD mortality. Associations were stronger for CVD mortality than for mortality due to cancer or other causes.

Mechanisms of Inflammation-Associated Depression: Immune Influences on Tryptophan and Phenylalanine Metabolisms

Metabolic parameters have a direct role in the regulation of immune cell function. Thereby the inflammation-induced metabolism of aromatic amino acids, most importantly of tryptophan and phenylalanine, plays a central role. In addition, neuropsychiatric conditions that go along with disorders that are characterized by acute or chronic inflammation, such as the development of depression, decreased quality of life or cognitive impairments, are connected to disturbed amino acid and subsequent neurotransmitter metabolism.The bioanalytical procedures for the determination of concentrations of tryptophan and phenylalanine and their respective first stable intermediates kynurenine and tyrosine as well as some analytical finesses and potential sources of errors are discussed in this chapter. Monitoring of these immunometabolic parameters throughout therapies in addition to biomarkers of immune response and inflammation such as neopterin can be useful to determine disease progression but also to plan psychiatric interventions timely, thus to establish personalized treatments.

Indoleamine 2,3-Dioxygenase Fine-Tunes Immune Homeostasis in Atherosclerosis and Colitis through Repression of Interleukin-10 Production

Indoleamine 2,3-dioxygenase 1 (Ido1) is a rate-limiting enzyme that catalizes the degradation of tryptophan along the kynurenine pathway. Here, we show that Ido1 activity sustains an immunostimulatory potential through inhibition of interleukin (Il)10. In atherosclerosis, Ido1-dependent inhibition of Il10 translates into disease exacerbation. The resistance of Ido1-deficient mice to enhanced immune activation is broken in Ido1/Il10 double-deficient mice, which show exaggerated immune responses and develop severe spontaneous colitis. We demonstrate that Ido1 activity is required for the regulation of Il10 and that kynurenic acid (Kna), an Ido1-derived metabolite, is responsible for reduced Il10 production through activation of a cAMP-dependent pathway and inhibition of Erk1/2 phosphorylation. Resupplementation of Ido1-deficient mice with Kna limits Il10 expression and promotes atherosclerosis. In human atherosclerotic lesions, increased levels of Kna are associated with an unstable plaque phenotype, and its blood levels predict death and recurrent myocardial infarction in patients with coronary artery disease.

Insufficient glucocorticoid signaling and elevated inflammation in coronary heart disease patients with comorbid depression

Coronary heart disease (CHD) and depression are very common and often co-existing disorders. In addition to psychological and social morbidity, depression exacerbates adverse cardiac outcomes in CHD patients. Inflammation has been proposed as one of the mechanisms involved in the association between these two debilitating diseases. Therefore, the present study aimed to evaluate inflammatory responses as well as to investigate the pathophysiological mechanisms underlying the putative inflammatory activation in CHD patients with and without depression, by assessing the function of two important biological factors regulating inflammation, the hypothalamus-pituitary-adrenal (HPA) axis and the glucocorticoid receptor (GR). Eighty-three CHD patients with (n=28) and without (n=55) comorbid depression were recruited from primary care services in South London. Depression status was assessed by means of Clinical Interview Schedule Revised for diagnosis of depression, and Beck Depression Inventory for the presence of depressive symptoms. Serum C-reactive protein (CRP), plasma vascular endothelial growth factor (VEGF), and plasma and salivary cortisol were measured using commercially available ELISA kits. Gene expression of GR and interleukin-6 (IL-6) were conducted via qPCR. GR sensitivity was evaluated in vitro in isolated peripheral blood mononuclear cells using the dexamethasone inhibition of lipopolysaccharide-stimulated IL-6 levels. Serum levels of kynurenine pathway metabolites were measured using high performance liquid chromatography. Our results show that CHD patients with depression had higher levels of CRP, IL-6 gene expression, and VEGF compared with CHD non-depressed, as well as lower plasma and saliva cortisol levels. The CHD depressed group also exhibited a reduction in GR expression and sensitivity. Finally, tryptophan levels were significantly lower in patients with depression, who also showed an increased kynurenine/tryptophan ratio. In conclusion, CHD patients with depression had elevated levels of inflammation in the context of HPA axis hypoactivity, GR resistance, and increased activation of the kynurenine pathway. Reduced cortisol bioavailability and attenuated glucocorticoid responsiveness due to decreased expression and sensitivity of GR may lead to insufficient glucocorticoid signaling and thus elevation of inflammation in these patients.

Neopterin as a Predictor of Functional Outcome and Mortality in Chinese Patients with Acute Ischemic Stroke

Immune responses and inflammation play an important role in the pathogenesis of ischemic stroke. We therefore evaluated the 6-month prognostic value of early measurement of serum neopterin levels, a marker of inflammation and immune system activation, in Chinese patients with acute ischemic stroke (AIS). Consecutive AIS patients admitted to the emergency department were identified. Clinical information was collected. Serum concentration of neopterin and NIH stroke scale (NIHSS) were measured at the time of admission. Functional outcome was measured by modified Rankin scale (mRS) 6 months after admission. Multivariate analyses were performed using logistic regression models. During the inclusion period, 312 patients with first-ever AIS were included and 290 completed follow-up. The results indicated that the serum neopterin levels were significantly (P < 0.0001) higher in acutely ischemic stroke patients as compared to normal controls. Neopterin was an independent prognostic marker of 6-month functional outcome and death [odds ratio (OR) 4.33 (1.83-10.32) and 6.68 (2.44-12.13), respectively, P < 0.0001 for both, adjusted for NIHSS, other predictors and vascular risk factors] in patients with AIS. Neopterin improved the area under the receiver operating characteristic curve of the NHISS score for functional outcome from 0.75 (95 % CI 0.69-0.83) to 0.85 (95 % CI 0.79-0.91; P < 0.001) and for mortality from 0.76 (95 % CI 0.68-0.85) to 0.87 (95 % CI 0.81-0.94; P < 0.001). Serum neopterin is a useful, independent tool to predict functional outcome and mortality 6 months after stroke.

Neopterin and 7,8-dihydroneopterin are generated within atherosclerotic plaques

Plasma neopterin correlates with the level of cardiovascular disease. Neopterin is the oxidation product of 7,8-dihydroneopterin, which is released by γ-interferon-stimulated macrophages. 7,8-Dihydroneopterin is a potent antioxidant, which inhibits lipid oxidation, macrophage cell death and scavenger receptor CD36 expression. The concentration of neopterin within atherosclerotic plaques was measured in tissue removed from carotid and femoral arteries. The excised plaques were cut into 3-mm-thick sections, and each section was analysed for neopterin, total neopterin, cholesterol, lipid peroxides, α-tocopherol and protein-bound 3,4-dihydroxyphenylalanine. Selected plaques were placed in tissue culture, and the media was analysed for 7,8-dihydroneopterin and neopterin release. Total neopterin levels ranged from 14 to 18.8 nmol/g of tissue. Large ranges of values were seen both within the same plaque and between plaques. No correlation between neopterin and any of the other analytes was observed, nor was there any significant trend in levels along the length of the plaques. γ-Interferon stimulation of cultured plaque generated total neopterin concentrations from 1 to 4 nmol/(g 24 h). The level of 7,8-dihydroneopterin generated within the plaque was within the range that inhibits lipid oxidation. The data show that atherosclerotic plaques are extremely dynamic in biochemistry and are the likely source of the plasma 7,8-dihydroneopterin and neopterin.

Improvement of blood inflammatory marker levels in patients with hypothyroidism under levothyroxine treatment

BACKGROUND

There are several specific inflammatory and oxidative correlates among patients with hypothyroidism, but most studies are cross-sectional and do not evaluate the change in parameters during the treatment. The aim of this study was to investigate the effect of levothyroxine replacement therapy on biomarkers of oxidative stress (OS) and systemic inflammation in patients with hypothyroidism.

METHODS

In this prospective open-label study, 17 patients with recently diagnosed primary hypothyroidism due to Hashimoto's thyroiditis who were not taking levothyroxine were included. The following parameters were measured before and at 6 and 12 months of levothyroxine treatment with an average dose of 1.5 to 1.7 μg/kg/day: thyroid-stimulating hormone (TSH), free thyroxine (FT4), high-sensitivity C-reactive protein (hs-CRP), interleukin 1 (IL-1), IL-6, IL-10, interferon gamma (INF-γ), tumor necrosis factor alpha (TNF-α), thiobarbituric acid-reactive substances (TBARS), activity of aminolevulinic acid dehydratase (δ-ALA-D), nonprotein and total thiol (NP-SH and T-SH) groups, total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C) and triglycerides (TG). Generalized estimating equation (GEE) modeling was used to analyze the effects of LRT (at pre-treatment, 6 months and 12 months) on those variables. The hypothyroidism status (i.e., overt or subclinical hypothyroidism) was included as a confounder in all analyses. An additional GEE post hoc analysis was made to compare time points.

RESULTS

There was a significant decrease in TSH over time (P < 0.0001), (initial levels were on average 32.4 μIU/mL and 10.5 μIU/mL at 12 months). There was a significant increase in FT4 (P < 0.0001) (initial levels were on average 0,8 ng/dL and 2.7 ng/dL at 12 months). There were significant changes in interleukin levels over time, with a significant increase in IL-10 (P < 0.0001) and significant decreases in IL-1 (P < 0.0001), IL-6 (P < 0.0001), INF-γ (P < 0.0001) and TNF-α (P < 0.0001). No significant difference in hs-CRP over time was observed (P < 0.284). There was a significant reduction in NP-SH (P < 0.0001).

CONCLUSIONS

This study observed significant changes in the inflammatory profile in hypothyroid patients under treatment, with reduction of pro-inflammatory cytokines and elevation of anti-inflammatory cytokine. In these patients, a decrease in low-grade chronic inflammation may have clinical relevance due to the known connection between chronic inflammation, atherosclerosis and cardiovascular events.

Regular consumption of black tea increases circulating kynurenine concentrations: A randomized controlled trial

BACKGROUND

Circulating neopterin and the ratio of kynurenine to tryptophan (KYN/TRP) concentrations are biomarkers of immune activation that have been linked to cardiovascular and total mortality. Several in vitro studies indicated that tea flavonoids and other antioxidants can modulate tryptophan breakdown rates and neopterin production in immune cells. We aimed to assess the effects of regular black tea consumption on tryptophan and neopterin metabolisms in vivo.

METHODS

Participants were healthy individuals, with no major illnesses and having normal to mildly elevated systolic blood pressure. They were randomly assigned to consume 3 cups/day of either powdered black tea solids (tea; n = 45) or a flavonoid-free caffeine-matched beverage (control; n = 49). Serum concentrations of tryptophan, kynurenine and neopterin were assessed at baseline and again at 3 and 6 months after daily ingestion of the respective beverage.

RESULTS

Regular consumption of tea over 6 months, compared to control, did not significantly alter neopterin (p = 0.13) or tryptophan (p = 0.85) concentrations, but did result in significantly higher kynurenine (p = 0.016) and KYN/TRP (p = 0.012). Relative to the control group, in the tea group kynurenine and KYN/TRP increased during the treatment period by 0.28 μmol/L (95% CI: - 0.04, 0.60) and 3.2 μmol/mmol (95% CI: - 1.6, 8.0), respectively at 3 months, and by 0.48 μmol/L (95% CI: 0.16, 0.80) and 7.5 μmol/mmol (95% CI: 2.5, 12.5), respectively at 6 months.

CONCLUSIONS

Increased circulation of kynurenine and KYN/TRP following regular black tea consumption may indicate enhanced tryptophan breakdown, possibly due to immune activation-induced tryptophan degrading enzyme indoleamine 2,3-dioxygenase.

GENERAL SIGNIFICANCE

The influence of black tea consumption on biomarkers of immune system activation could relate to its general health benefits. Data suggests that the net effect strongly depends on the individual immune state, being stimulatory in healthy individuals, while acting more immune dampening in situations with an inflammatory background.

Tryptophan catabolism and vitamin B-6 status are affected by gender and lifestyle factors in healthy young adults

BACKGROUND

Abnormalities of tryptophan (Trp) metabolism through the kynurenine (Kyn) pathway have been reported in various diseases; however, nutritional and lifestyle factors that affect this pathway in healthy individuals are not well documented.

OBJECTIVE

Our aim was to examine the effect of vitamin B-6 status and lifestyle factors including the use of vitamin B-6 supplements, alcohol, smoking, and oral contraceptives on Trp and its Kyn metabolites in a cohort of 2436 healthy young adults aged 18-28 y.

METHODS

Anthropometric and lifestyle data were collected by questionnaire. Participants provided blood samples for analysis of Trp, Kyn, anthranilic acid, kynurenic acid (KA), 3-hydroxykynurenine (HK), 3-hydroxyanthranilic acid (HAA), and xanthurenic acid (XA). Vitamin B-6 species were also measured.

RESULTS

Serum Trp metabolites were 10-15% higher among men (n = 993) compared with women (n = 1443; P < 0.0001), except for HK and XA. In all participants, serum Trp was positively associated with plasma pyridoxal 5'-phosphate (PLP; r = 0.28, P < 0.0001), reaching a plateau at PLP concentrations of ∼83 nmol/L. HK was inversely associated with PLP (r = -0.14, P < 0.01). Users of vitamin B-6 supplements (n = 671) had 6% lower concentrations of HK than nonusers (n = 1765; P = 0.0006). Oral contraceptive users (n = 385) had lower concentrations of KA (20.7%) but higher XA (24.1%) and HAA (9.0%) than did nonusers (n = 1058; P < 0.0001). After adjustment for gender and other lifestyle variables, XA concentrations were 16% higher in heavy drinkers (n = 713) than in never or occasional drinkers (n = 975; P = 0.0007). Concentrations of 2 other essential amino acids, methionine and arginine, also were positively associated with serum Trp (r = 0.65 and 0.33, respectively; P < 0.0001).

CONCLUSIONS

In this population of healthy young adults, gender has the largest influence on serum Kyn metabolite concentrations. The significant covariance of Trp with unrelated amino acids suggests that protein intake may be an important consideration in evaluating Kyn metabolism.

Low serum tryptophan predicts higher mortality in cardiovascular disease

BACKGROUND

The essential amino acid tryptophan is required for protein synthesis and formation of the neurotransmitter serotonin and may exert immunoregulatory functions. An accelerated tryptophan breakdown rate is associated with inflammation and immune activation.

MATERIALS AND METHODS

Serum concentrations of free tryptophan, neopterin and high-sensitivity C-reactive protein (hsCRP) were measured in 1196 patients with coronary artery disease (CAD) derived from the LUdwigshafen RIsk and Cardiovascular Health (LURIC) study.

RESULTS

Tryptophan concentrations did not differ between patients with (mean ± SD: 40.1 ± 9.8 μM) or without (42.3 ± 23.9 μM; not significant, Welch's test) angiographic CAD, but patients with CAD had higher neopterin (9.1 ± 8.2 nM) and hsCRP (9.3 ± 18.5 mg/L) concentrations compared to patients without (neopterin: 7.6 ± 4.7 nM, hsCRP: 5.8 ± 7.6 mg/L; both P < 0.0001). There existed an inverse correlation between serum tryptophan and neopterin (Spearman's rank correlation: rs = -0.273) and hsCRP (rs = -0.163; both P < 0.0001) concentrations. Median observation time was 10.5 years, and 385 patients had died, including 244 patients due to cardiovascular and 132 due to noncardiovascular causes. After adjustments for cardiovascular risk factors and other possible confounders, the hazard ratio (with 95% CI) in the first tryptophan quartile of the study population was 1.51 (1.19-1.90; P = 0.0006) for total mortality, 1.41 (1.05-1.89; P = 0.0224) for cardiovascular and 1.79 (1.20-2.67; P = 0.0042) for noncardiovascular mortalities, respectively, thus indicating a significantly higher risk of death in patients with tryptophan concentrations < 34 μM.

CONCLUSIONS

Low serum tryptophan in patients with CAD is associated with immune activation and indicates reduced life expectancy.

Associations of Plasma Kynurenines With Risk of Acute Myocardial Infarction in Patients With Stable Angina Pectoris

Objective—

Enhanced tryptophan degradation, induced by the proinflammatory cytokine interferon-γ, has been related to cardiovascular disease progression and insulin resistance. We assessed downstream tryptophan metabolites of the kynurenine pathway as predictors of acute myocardial infarction in patients with suspected stable angina pectoris. Furthermore, we evaluated potential effect modifications according to diagnoses of pre-diabetes mellitus or diabetes mellitus.

Approach and Results—

Blood samples were obtained from 4122 patients (median age, 62 years; 72% men) who underwent elective coronary angiography. During median follow-up of 56 months, 8.3% had acute myocardial infarction. Comparing the highest quartile to the lowest, for the total cohort, multivariable adjusted hazard ratios (95% confidence intervals) were 1.68 (1.21–2.34), 1.81 (1.33–2.48), 1.68 (1.21–2.32), and 1.48 (1.10–1.99) for kynurenic acid, hydroxykynurenine, anthranilic acid, and hydroxyanthranilic acid, respectively. The kynurenines correlated with phenotypes of the metabolic syndrome, and risk associations were generally stronger in subgroups classified with pre-diabetes mellitus or diabetes mellitus at inclusion ( P int ≤0.05). Evaluated in the total population, hydroxykynurenine and anthranilic acid provided statistically significant net reclassification improvements (0.21 [0.08–0.35] and 0.21 [0.07–0.35], respectively).

Conclusions—

In patients with suspected stable angina pectoris, elevated levels of plasma kynurenines predicted increased risk of acute myocardial infarction, and risk estimates were generally stronger in subgroups with evidence of impaired glucose homeostasis. Future studies should aim to clarify roles of the kynurenine pathway in atherosclerosis and glucose metabolism.

Vitamins B2and B6as determinants of kynurenines and related markers of interferon-γ-mediated immune activation in the community-based Hordaland Health Study

Vitamins B2and B6are cofactors in the kynurenine pathway. Many of the kynurenines are neuroactive compounds with immunomodulatory effects. In the present study, we aimed to investigate plasma concentrations of vitamins B2and B6as determinants of kynurenines and two markers of interferon-γ-mediated immune activation (kynurenine:tryptophan ratio (KTR) and neopterin). We measured the concentrations of vitamins B2and B6vitamers, neopterin, tryptophan and six kynurenines (i.e. kynurenine, anthranilic acid, kynurenic acid, 3-hydroxykynurenine, 3-hydroxyanthranilic acid and xanthurenic acid) in plasma from 7051 individuals. Dietary intake of vitamins B2and B6was assessed using a validated FFQ. Associations were investigated using partial Spearman's correlations, generalised additive models, and segmented or multiple linear regression. The B2vitamer, riboflavin, was positively associated with 3-hydroxyanthranilic acid and xanthurenic acid, with correlation coefficients, as obtained by segmented regression, of 0·20 (95 % CI 0·16, 0·23) and 0·24 (95 % CI 0·19, 0·28), at riboflavin concentrations below the median value (13·0 nmol/l). The vitamin B6vitamer, pyridoxal 5′-phosphate (PLP), was positively associated with most kynurenines at PLP concentrations < 39·3–47·0 nmol/l, and inversely associated with 3-hydroxykynurenine with the association being more prominent at PLP concentrations < 18·9 nmol/l. Riboflavin and PLP were associated with xanthurenic acid only at relatively low, but normal concentrations of both vitamers. Lastly, PLP was negatively correlated with neopterin and KTR. These results demonstrate the significant and complex determination of kynurenine metabolism by vitamin status. Future studies on B-vitamins and kynurenines in relation to chronic diseases should therefore integrate data on relevant biomarkers related to B-vitamins status and tryptophan metabolism.

Interferon gamma (IFN-γ)-mediated inflammation and the kynurenine pathway in relation to risk of hip fractures: the Hordaland Health Study

The cytokine interferon gamma (IFN-γ) stimulates neopterin release and tryptophan degradation into kynurenines through the kynurenine pathway. High levels of neopterin were associated with increased hip fracture risk, as were some of the kynurenines, suggesting a role of IFN-γ-mediated inflammation in the processes leading to hip fracture.

INTRODUCTION

Low-grade systemic inflammation has been associated with bone loss and risk of fractures. Interferon gamma (IFN-γ) initiates macrophage release of neopterin and also stimulates degradation of tryptophan along the kynurenine pathway as part of cell-mediated immune activation. Plasma neopterin and the kynurenine/tryptophan ratio (KTR) are thus markers of IFN-γ-mediated inflammation. Risk of hip fracture was investigated in relation to markers of inflammation and metabolites in the kynurenine pathway (kynurenines).

METHODS

Participants (71 to 74 years, N = 3,311) in the community-based Hordaland Health Study (HUSK) were followed for hip fractures from enrolment (1998-2000) until 31 December 2009. Plasma C-reactive protein (CRP), neopterin, KTR, and six kynurenines were investigated as predictors of hip fracture, using Cox proportional hazards regression analyses.

RESULTS

A hazard ratio (HR) of 1.9 (95% confidence interval (CI) 1.3-2.7) for hip fracture was found in the highest compared to the lowest quartile of neopterin (p trend across quartiles <0.001). CRP and KTR were not related to hip fracture risk. Among the kynurenines, a higher risk of fracture was found in the highest compared to the lowest quartiles of anthranilic acid and 3-hydroxykynurenine. For subjects in the highest quartiles of neopterin, CRP, and KTR compared to those in no top quartiles, HR was 2.5 (95% CI 1.6-4.0).

CONCLUSIONS

This may indicate a role for low-grade immune activation in the pathogenic processes leading to hip fracture.

Interferon-γ-induced inflammatory markers and the risk of cancer: the Hordaland Health Study

BACKGROUND

It has been reported that interferon-γ (IFN-γ)-induced inflammatory markers, such as circulating neopterin and kynurenine-to-tryptophan ratio (KTR), are increased in patients with cancer and are also a predictor of poor prognosis. However, whether baseline levels of these makers are associated with subsequent cancer risk in the general population remains unknown.

METHODS

We conducted a prospective analysis of the Hordaland Health Study in 6594 adults without known cancer at baseline who were enrolled between April 1998 and June 1999. Hazard ratios (HRs) and 95% confidence intervals (CIs) were calculated using multivariate Cox proportional hazards regression models adjusted for sex, age, body mass index, smoking status, and renal function.

RESULTS

A total of 971 incident cancer cases (507 men and 464 women) were identified over a median follow-up time of 12 years. Baseline plasma neopterin, KTR and C-reactive protein (CRP) were significantly associated with an increased risk of overall cancer in models adjusted for covariates (P for trend across quartiles = .006 for neopterin, .022 for KTR, and .005 for CRP). The multivariate-adjusted HR (95% CI) per SD increment in similar models were 1.09 (1.03-1.16) for neopterin, 1.07 (1.01-1.14) for KTR, and 1.04 (0.98-1.10) for CRP. The associations between the inflammatory markers and risk of major specific cancer types were also provided.

CONCLUSIONS

Our findings indicate that plasma neopterin, KTR, and CRP are associated with a significantly increased risk of overall cancer. Our study revealed novel evidence regarding the role of IFN-γ-induced inflammation in human carcinogenesis.

Interferon (IFN)-γ-mediated inflammation and the kynurenine pathway in relation to bone mineral density: the Hordaland Health Study

The risk of osteoporosis increases in inflammatory disorders. In cell-mediated immune activation, interferon (IFN)-γ stimulates macrophage release of neopterin and increases the activity of indoleamine 2,3-dioxygenase (IDO), thereby stimulating tryptophan degradation along the kynurenine pathway. Plasma levels of neopterin and the kynurenine/tryptophan ratio (KTR) are thus markers of IFN-γ-mediated inflammation. Several kynurenine pathway metabolites (kynurenines) possess immunomodulatory properties. The aim of this study was to investigate associations between markers of IFN-γ-mediated inflammation and kynurenines with bone mineral density (BMD). The community-based Hordaland Health Study (HUSK), with middle-aged (46–49 years) and older (71–74 years) participants, was conducted from 1998 to 2000 (n = 5312). Hip BMD in relation to neopterin, KTR and kynurenines were investigated, using linear and logistic regression analyses. In the oldest group, neopterin (P ≤ 0·019) and KTR (P ≤ 0·001) were associated inversely with BMD after multiple adjustment. Comparing the highest to the lowest quartiles, the odds ratios of low BMD (being in the lowest quintile of BMD) in the oldest cohort were for neopterin 2·01 among men and 2·34 among women (P ≤ 0·007) and for KTR 1·80 for men and 2·04 for women (P ≤ 0·022). Xanthurenic acid was associated positively with BMD in all sex and age groups while 3-hydroxyanthranilic acid was associated positively with BMD among women only (P ≤ 0·010). In conclusion, we found an inverse association between BMD and markers of IFN-γ-mediated inflammation in the oldest participants. BMD was also associated with two kynurenines in both age groups. These results may support a role of cell-mediated inflammation in bone metabolism.

Immunological alterations in individuals exposed to metal(loid)s in the Panasqueira mining area, Central Portugal

Environmental studies performed in Panasqueira mine area (central Portugal) identified high concentrations of several metal(loid)s in environmental media, and individuals environmentally and occupationally exposed showed higher levels of As, Cr, Mg, Mn, Mo, Pb and Zn in blood, urine, hair and nails when compared to unexposed controls. To evaluate the presence of immunological alterations attributable to environmental contamination, we quantified neopterin, kynurenine, tryptophan, and nitrite concentrations in plasma, and analysed the percentage of several lymphocytes subsets, namely CD3(+), CD4(+) and CD8(+) T-cells, CD19(+) B-cells, and CD16(+)56(+) natural killer (NK) cells in a group of individuals previously tested for metal(loid) levels in different biological matrices. The environmentally exposed group had significantly lower levels of %CD8(+) and higher CD4(+)/CD8(+) ratios, whereas the occupationally exposed individuals showed significant decreases in %CD3(+) and %CD4(+), and significant increases in %CD16(+)56(+), when compared to controls. Analysed biomarkers were found to be influenced by age, particularly neopterin, kynurenine and kynurenine to tryptophan ratio (Kyn/Trp) with significantly higher levels in older individuals, and %CD3(+), %CD8(+) and %CD19(+) with significantly lower values in older individuals. Males environmentally exposed showed significantly lower values of %CD19(+) when compared to control females. The concentration of Pb in toenails was associated to the level of neopterin, kynurenine and Kyn/Trp ratio (all direct), and the concentration of Mn in blood to the level of %CD8(+), %CD19(+) (both inverse) and CD4(+)/CD8(+) ratio (direct). Overall our results show that the metal(loid) contamination in Panasqueira mine area induced immunotoxic effects in exposed populations, possibly increasing susceptibility to diseases.

Immune activation and inflammation in patients with cardiovascular disease are associated with higher phenylalanine to tyrosine ratios: the ludwigshafen risk and cardiovascular health study

Higher serum neopterin is associated with increased mortality in patients with coronary artery disease (CAD). Preferentially Th1-type cytokine interferon-γ stimulates neopterin production by GTP cychlohydrolase I (GCH-I) in parallel in monocyte-derived macrophages and dendritic cells. In other cells, activation of GCH-I leads to the formation of 5,6,7,8-tetrahydrobiopterin (BH₄), the necessary cofactor of amino acid hydroxylases like phenylalanine 4-hydroxylase (PAH). Serum concentrations of phenylalanine, tyrosine, neopterin, and high sensitivity C-reactive protein (hsCRP) were measured in 1196 patients derived from the LUdwigshafen RIsk and Cardiovascular Health (LURIC) study, a cohort study among patients referred for coronary angiography. The phenylalanine to tyrosine ratio (Phe/Tyr) served as an estimate of phenylalanine hydroxylase (PAH) enzyme activity. Serum concentrations of phenylalanine and tyrosine and of Phe/Tyr did not differ between individuals with or without CAD (Welch's t-test: P = n.s.). Higher neopterin and hsCRP concentrations were observed in CAD patients compared to controls (P < 0.0001) and they correlated with Phe/Tyr (Spearman's rank correlation for neopterin: r_s = 0.216 and hsCRP: r_s = 0.122; both of P < 0.0001) concentrations. In conclusion, immune activation is associated with higher Phe/Tyr in CAD patients. Data indicates subnormal PAH activity which might be involved in the precipitation of neuropsychiatric symptoms in patients.

Immunomodulatory properties of cacao extracts - potential consequences for medical applications

Anti-inflammatory properties of cacao, fruits of Theobroma cacao L. (Sterculiaceae), are well documented, and therapeutic applications are described for gastrointestinal, nervous, and cardiovascular abnormalities. Most, if not all of these disease conditions involve inflammation or immune activation processes. The pro-inflammatory cytokine interferon-γ (IFN-γ) and related biochemical pathways like tryptophan breakdown by indoleamine 2,3-dioxygenase (IDO) and neopterin formation are deeply involved in their pathogenesis. Neopterin concentrations and the kynurenine to tryptophan ratio (Kyn/Trp, an estimate of IDO activity) are elevated in a significant proportion of patients with virus infections, cancer, autoimmune syndrome, neurodegeneration, and coronary artery disease. Moreover, higher neopterin and Kyn/Trp concentrations are indicative for poor prognosis. When investigating the effect of aqueous or ethanolic extracts of cacao on IFN-γ, neopterin and Kyn/Trp concentrations in mitogen-stimulated human peripheral blood mononuclear cells, breakdown of tryptophan by IDO, and formation of neopterin and IFN-γ were dose-dependently suppressed. The effects observed in the cell-based assays are associated with the antioxidant activity of the cacao extracts as determined by the cell-free oxygen radical absorption capacity assay. The influence of cacao extracts on IDO activity could be of particular relevance for some of the beneficial health effects ascribed to cacao: tryptophan breakdown by IDO is strongly involved in immunoregulation, and the diminished availability of tryptophan limits the biosynthesis of neurotransmitter serotonin. The inhibition of tryptophan breakdown by cacao constituents could thus be relevant not only for immune system restoration in patients, but also contribute to mood elevation and thereby improve quality of life. However, the available data thus far are merely in vitro only and future studies need to investigate the influence of cacao on tryptophan metabolism in vivo.

Interferon-gamma increases the ratio of matrix metalloproteinase-9/tissue inhibitor of metalloproteinase-1 in peripheral monocytes from patients with coronary artery disease

Acute coronary syndromes (ACS) may be triggered by acute infections. Systemic production of interferon gamma (IFN-γ) is induced during infection and regulates the production of matrix metalloproteinases (MMPs) and their inhibitors (TIMPs), both important in plaque stability. This study evaluates the effect of IFN-γ on the MMPs/TIMP-1 ratio in cultured monocytes from 30 patients with stable coronary artery disease (CAD), 30 with unstable angina (UA) or non-ST-segment elevation myocardial infarction (NSTEMI), and 30 healthy blood donors. Supernatant concentrations of MMP-1, -2, -9, and TIMP-1 were measured by enzyme-linked immunoassays. Basal concentration of MMP-1 and TIMP-1 was similar between groups, while MMP-2 was higher in healthy individuals and MMP-9 in patients with UA/NSTEMI. Upon IFN-γ stimulation, MMP-9 secretion increased in all groups, while TIMP-1 decreased only in patients with CAD, which in turn result in a strikingly elevation in their mean MMP-9/TIMP-1 ratio. MMP-1/TIMP-1 and MMP-2/TIMP-1 ratios were <1.0 in basal conditions and after stimulation in all groups. Our results suggest that nonstimulated monocytes from patients with stable CAD show a similar behavior than those from healthy individuals. However, stimulation with IFN-γ induces an increase on the MMP-9/TIMP-1 ratio as high as that found in patients with ACS. Thus, it may bring biological plausibility to the association between acute infections and the development of ACS.

Mechanistic perspective on the relationship between pyridoxal 5'-phosphate and inflammation

A variety of inflammatory disease conditions have been found to be associated with low levels of plasma pyridoxal 5'-phosphate (PLP), the active form of vitamin B6 , without any indication of a lower dietary intake of vitamin B6 , excessive catabolism of the vitamin, or congenital defects in its metabolism. The present review was conducted to examine the existing literature in this regard. Current evidence suggests that the inverse association between plasma PLP and inflammation may be the result of mobilization of this coenzyme to the site of inflammation, for use by the PLP-dependent enzymes of the kynurenine pathway of tryptophan degradation, metabolism of the immunomodulatory sphingolipids, ceramide and sphingosine 1-phosphate, and for serine hydroxymethylase for immune cell proliferation.

Vitamin B6 status and interferon-γ-mediated immune activation in primary hyperparathyroidism

OBJECTIVES

Primary hyperparathyroidism (PHPT) has been associated with low-grade inflammation and elevated risk of cardiovascular disease (CVD). In inflammatory conditions, interferon-γ (IFN-γ) activity is enhanced and a decreased circulating concentration of vitamin B6 is often observed. Such changes in IFN-γ activity or vitamin B6 levels have been associated with increased incidence of CVD. The aim of the study was to investigate systemic markers of IFN-γ-mediated immune activation, such as neopterin, the kynurenine-to-tryptophan ratio (KTR) and kynurenine pathway metabolites, as well as B6 vitamers in patients with PHPT.

DESIGN/SUBJECTS

A total of 57 patients with PHPT and a control group of 20 healthy blood donors were included in this study. PHPT patients who responded positively to parathyroidectomy were followed for 6 months. Forty-three patients participated in the longitudinal study in which blood samples were taken at inclusion and 1, 3 and 6 months after surgery.

RESULTS

Plasma concentrations of the B6 vitamers pyridoxal 5'-phosphate (PLP) (P = 0.007) and pyridoxal (P = 0.013) were significantly lower in the patient group compared to healthy control subjects. An increase in the KTR indicated that the kynurenine pathway of tryptophan metabolism was altered in PHPT patients (P = 0.015). During the initial 6 months after surgery, levels of PLP (P < 0.001) and anthranilic acid (P < 0.001) increased significantly, whereas neopterin decreased (P = 0.018).

CONCLUSIONS

The results of this study demonstrate altered levels of vitamin B6 and the KTR in PHPT patients, both of which may reflect cellular immune activation. These abnormalities should be considered in relation to the increased risk of CVD previously observed in patients with PHPT.

Association between serum neopterin and inflammatory activation in chronic kidney disease

Background. The serum levels of neopterin, a marker associated with cell-mediated immunity are elevated in chronic kidney disease (CKD). We evaluated serum neopterin levels and investigated its association with markers of inflammation in a cross-section of CKD subjects without known cardiovascular disease. Methods. Serum neopterin levels were measured in 118 patients with stage 3–5 CKD and 41 healthy subjects with normal kidney function (HC). Patients with known cardiovascular disease were excluded. We also estimated highly sensitive CRP (hsCRP) and interluekin-6 (IL-6), tumor necrosis factor-α (TNF-α) and interferon-γ (IFN-γ) in the CKD subjects. All assays were done using commercially available ELISA kits. The correlation between neopterin and markers of inflammation were investigated. Results. Of the CKD population, 82 were in stage 5 (60 stage 5 D), 24 in stage 4, and 12 in stage 3. The mean age was 51.04 ± 1.3 years and 66% were males. The commonest cause of CKD was diabetes (36%). Serum neopterin levels were 5-fold higher in CKD patients as compared to HC (74.8 ± 3.6 versus 15.0 ± 2.8 nmol/L, P < 0.0001). There was a graded increase of serum neopterin from stages 3 to 4 and 5. CKD 5 D patients exhibited significantly higher levels compared to nondialysis stage 5 patients (P < 0.0001). An inverse correlation was noted between serum neopterin and eGFR (r = −0.359, P < 0.0001). Serum neopterin correlated with hsCRP (r = 0.285, P = 0.002), IL-6 (r = 0.212, P = 0.034), and IFN-γ (r = 0.32, P = 0.001) but not with TNF-α. Conclusion. Serum neopterin level is elevated and correlates with the severity of CKD. The elevation correlates with elevation of most, but not all, inflammatory markers. Its role in future development of cardiovascular disease and modulation with anti-inflammatory therapies needs further studies.

Persistent accumulation of interferon-γ-producing CD8+CD56+ T cells in blood from patients with coronary artery disease

OBJECTIVE

There is emerging evidence for CD8(+) T cell alterations in blood from patients with coronary artery disease (CAD). We examined whether the distribution and phenotype of CD8(+)CD56(+) T cells differed according to the clinical manifestation of CAD.

METHODS

Patients with acute coronary syndrome (ACS, n = 30), stable angina (SA, n = 34) and controls (n = 36) were included. Blood was collected before and up to 12 months after referral for coronary investigation. CD8(+)CD56(+) T cells were assessed by flow cytometry for expression of surface markers, apoptosis, and intracellular expression of cytokines.

RESULTS

The proportions of CD8(+)CD56(+) T cells were significantly higher in both ACS and SA patients compared with controls, and remained so after 3 and 12 months. This was independent of age, sex, systemic inflammation and cytomegalovirus seropositivity. CD8(+)CD56(+) T cells differed from CD8(+)CD56(-) T cells in terms of lower CD28 expression and fewer apoptotic cells. Both CD8(+) T cell subsets were positive for interferon (IFN)-γ and tumor necrosis factor, although IFN-γ was significantly more confined to the CD8(+)CD56(+) T cells.

CONCLUSION

The persistent accumulation of CD8(+)CD56(+) T cells in ACS and SA patients share several features with immunological aging. It also contributes to a larger IFN-γ(+) pool in blood, and may thereby hypothetically drive the atherosclerotic process in a less favorable direction.

Picolinic acid in patients with chronic hepatitis C infection: a preliminary report

Macrophage activation seems to be a feature of chronic liver diseases. Picolinic acid (PA) as a macrophage secondary signal causes the activation of interferon-gamma- (IFN-γ-) prime macrophage and triggers cytokine-driven inflammatory reactions. The rationale for seeking increased PA formation in chronic viral hepatitis is based on the involvement of activated macrophages in chronic viral hepatitis-associated inflammation. The aim of this study was to determine serum PA levels in patients with chronic hepatitis C infection, taking into account the presence of diabetes. We assessed PA and high-sensitivity C-reactive protein (hsCRP) as a marker of inflammation in 51 patients with chronic hepatitis C infection (CHC), both with and without diabetes and 40 controls. Compared with the controls, the patients with CHC showed a significant increase in plasma concentrations of PA and hsCRP (P < 0.01 and P < 0.05, resp.). The values of PA and hsCRP were more elevated in patients with diabetes than without diabetes (both P < 0.01). The positive relationships were between PA and hsCRP levels (P < 0.05) and the presence of diabetes (P < 0.001). We documented that significant elevation in serum PA levels is associated with diabetes prevalence and increased inflammatory response reflected in hsCRP levels in CHC patients.

Acute coronary events

In the United States alone, more than 400,000 Americans die annually from coronary artery disease and more than 1,000,000 suffer acute coronary events, i.e., myocardial infarction and sudden cardiac death.1 Considering the aging of our population and increasing incidence of diabetes and obesity, the morbidity from coronary artery disease, and its associated costs, will place an increasing, substantial burden on our society.2 Between 2010 and 2030, total direct medical costs spent in the US for cardiovascular diseases are projected to triple from 273 to 818 billion dollars.2 Although effective treatments are available and considerable efforts are ongoing to identify new strategies for the prevention of coronary events, predicting such events in an individual has been challenging.3 In hopes of improving our ability to determine the risk of coronary events, it is prudent to review our knowledge of factors that lead to acute coronary events.

Plasma indoleamine 2,3-dioxygenase concentration is increased in hemodialysis patients and may contribute to the pathogenesis of coronary heart disease

INTRODUCTION

Coronary heart disease (CHD) is the leading cause of death in hemodialysis (HD) patients. Inflammation contributes to the pathogenesis of atherosclerosis in this population. Indoleamine 2,3-dioxygenase (IDO), an enzyme with immunomodulatory properties, was evaluated in HD patients with or without CHD.

METHODS

Of the total of 66 HD patients, 22 of them with CHD were confirmed by coronary angiography and 24 healthy volunteers were enrolled in the study. Plasma IDO was assessed by means of enzyme-linked immunosorbent assay. Serum interleukin-6 (IL-6) and C-reactive protein (CRP) were also measured.

RESULTS

Compared with healthy volunteers, plasma IDO concentration was markedly increased in HD patients (median 8.04 ng/mL vs. 48.9 ng/mL). Serum IL-6 and CRP were also significantly increased in HD patients. Compared with HD patients without CHD, plasma IDO concentration was significantly increased in HD patients with CHD (median 38.6 ng/mL vs. 74.5 ng/mL). Neither IL-6 nor CRP differed between the last two groups. IDO was negatively correlated with IL-6 and CRP.

CONCLUSION

IDO concentration is increased in HD patients and is increased further in HD patients with CHD. It remains to be elucidated if increased IDO plays a direct role in the pathogenesis of atherosclerosis or if it affects atherosclerosis indirectly by curtailing chronic inflammation or both.