Association of the kynurenine pathway of tryptophan metabolism with HIV-related gut microbiota alterations and visceral adipose tissue accumulation

BACKGROUND

The aim of the study was to investigate the association between HIV-related gut microbiota changes, alterations in the Kyn pathway of Trp metabolism and visceral adipose tissue in the context of HIV infection.

METHODS

383 people with HIV (PWH) were included from the COCOMO study. Gut microbiota composition was analyzed by 16S ribosomal RNA sequencing. Plasma metabolites were analyzed by LC-MS/MS. Visceral (VAT) and subcutaneous (SAT) adipose tissue areas were measured by single slice CT scan (4 th lumbar vertebra).

RESULTS

HIV-related gut microbiota alterations were associated with lower tryptophan (β -0.01 [-0.03;-0.00]) and higher kynurenine-to-tryptophan ratio (β 0.03 [95% CI, 0.01;0.05]), which in turn was associated with higher VAT-to-SAT ratio (β 0.50 [0.10;0.90]) and larger VAT area (β 30.85 [4.43;57.28]). In mediation analysis, kynurenine-to-tryptophan ratio mediated 10% (p-value 0.023) of the association between VAT-to-SAT ratio and HIV-related gut microbiota.

CONCLUSIONS

Our data suggest HIV-related gut microbiota compositional changes and gut microbial translocation as potential drivers of high kynurenine-to-tryptophan ratio in PWH. In turn, increased activity in the kynurenine pathway of tryptophan metabolism was associated with larger visceral adipose tissue area. Taken together, our findings may suggest a possible role for this pathway in the gut-adipose tissue axis in the context of HIV infection.

Vitamin B6 catabolism and lung cancer risk: results from the Lung Cancer Cohort Consortium (LC3)

BACKGROUND

Increased vitamin B6 catabolism related to inflammation, as measured by the PAr index (the ratio of 4-pyridoxic acid over the sum of pyridoxal and pyridoxal-5'-phosphate), has been positively associated with lung cancer risk in two prospective European studies. However, the extent to which this association translates to more diverse populations is not known.

MATERIALS AND METHODS

For this study, we included 5323 incident lung cancer cases and 5323 controls individually matched by age, sex, and smoking status within each of 20 prospective cohorts from the Lung Cancer Cohort Consortium. Cohort-specific odds ratios (ORs) and 95% confidence intervals (CIs) for the association between PAr and lung cancer risk were calculated using conditional logistic regression and pooled using random-effects models.

RESULTS

PAr was positively associated with lung cancer risk in a dose-response fashion. Comparing the fourth versus first quartiles of PAr resulted in an OR of 1.38 (95% CI: 1.19-1.59) for overall lung cancer risk. The association between PAr and lung cancer risk was most prominent in former smokers (OR: 1.69, 95% CI: 1.36-2.10), men (OR: 1.60, 95% CI: 1.28-2.00), and for cancers diagnosed within 3 years of blood draw (OR: 1.73, 95% CI: 1.34-2.23).

CONCLUSION

Based on pre-diagnostic data from 20 cohorts across 4 continents, this study confirms that increased vitamin B6 catabolism related to inflammation and immune activation is associated with a higher risk of developing lung cancer. Moreover, PAr may be a pre-diagnostic marker of lung cancer rather than a causal factor.

No association between circulating concentrations of vitamin D and risk of lung cancer: an analysis in 20 prospective studies in the Lung Cancer Cohort Consortium (LC3)

Background

There is observational evidence suggesting that high vitamin D concentrations may protect against lung cancer. To investigate this hypothesis in detail, we measured circulating vitamin D concentrations in prediagnostic blood from 20 cohorts participating in the Lung Cancer Cohort Consortium (LC3).

Patients and methods

The study included 5313 lung cancer cases and 5313 controls. Blood samples for the cases were collected, on average, 5 years before lung cancer diagnosis. Controls were individually matched to the cases by cohort, sex, age, race/ethnicity, date of blood collection, and smoking status in five categories. Liquid chromatography coupled with tandem mass spectrometry was used to separately analyze 25-hydroxyvitamin D2 [25(OH)D2] and 25-hydroxyvitamin D3 [25(OH)D3] and their concentrations were combined to give an overall measure of 25(OH)D. We used conditional logistic regression to calculate odds ratios (ORs) and 95% confidence intervals (CIs) for 25(OH)D as both continuous and categorical variables.

Results

Overall, no apparent association between 25(OH)D and risk of lung cancer was observed (multivariable adjusted OR for a doubling in concentration: 0.98, 95% CI: 0.91, 1.06). Similarly, we found no clear evidence of interaction by cohort, sex, age, smoking status, or histology.

Conclusion

This study did not support an association between vitamin D concentrations and lung cancer risk.

Association of plasma neopterin with risk of an inpatient hospital diagnosis of atrial fibrillation: results from two prospective cohort studies

BACKGROUND

Link between inflammation and atrial fibrillation (AF) has been increasingly recognized. Neopterin, a biomarker of cellular immune activation, may be associated with incident AF.

OBJECTIVE

To investigate the association between plasma neopterin levels and risk of an inpatient hospital diagnosis of AF, and to evaluate a joint association of neopterin and a nonspecific inflammatory marker C-reactive protein (CRP) in two prospective cohorts.

METHODS

We performed a prospective analysis from a community-based cohort (the Hordaland Health Study (HUSK), n = 6891), and validated the findings in a cohort of patients with suspected stable angina pectoris (the Western Norway Coronary Angiography Cohort (WECAC), n = 2022).

RESULTS

In both cohorts, higher plasma levels of neopterin were associated with an increased risk of incident AF after adjustment for age, sex, body mass index, current smoking, diabetes, hypertension and renal function. The multivariable-adjusted hazard ratio (HR) (95% CI) per one SD increment of log-transformed neopterin was 1.20 (1.10-1.32) in HUSK and 1.26 (1.09-1.44) in WECAC. Additional adjustment for CRP did not materially affect the risk association for neopterin. The highest risk of AF was found among individuals with both neopterin and CRP levels above the median (HR: 1.54; 95% CI: 1.16-2.05 in HUSK and HR: 1.67; 95% CI: 1.11-2.52 in WECAC).

CONCLUSIONS

Our findings indicate an association of plasma neopterin with risk of an inpatient hospital diagnosis of AF, which remains after adjustment for traditional risk factors as well as for CRP. This study highlights a role of cellular immune activation, in addition to inflammation, in AF pathogenesis.

Smoking, plasma cotinine and risk of atrial fibrillation: the Hordaland Health Study

BACKGROUND

Cigarette smoking has been identified as a major modifiable risk factor for coronary heart disease and mortality. However, findings on the relationship between smoking and atrial fibrillation (AF) have been inconsistent. Furthermore, findings from previous studies were based on self-reported smoking.

OBJECTIVE

To examine the associations of smoking status and plasma cotinine levels, a marker of nicotine exposure, with risk of incident AF in the Hordaland Health Study.

METHODS

We conducted a prospective analysis of 6682 adults aged 46-74 years without known AF at baseline. Participants were followed via linkage to the Cardiovascular Disease in Norway (CVDNOR) project and the Cause of Death Registry. Smoking status was assessed by both questionnaire and plasma cotinine levels.

RESULTS

A total of 538 participants developed AF over a median follow-up period of 11 years. Using questionnaire data, current smoking (HR: 1.41, 95% CI: 1.09-1.83), but not former smoking (HR: 1.03, 95% CI: 0.83-1.28), was associated with an increased risk of AF after adjustment for gender, age, body mass index, hypertension, physical activity and education. Using plasma cotinine only, the adjusted HR (95% CI) was 1.40 (1.12-1.75) for participants with cotinine ≥85 nmol L^-1 compared to those with cotinine <85 nmol L^-1 . However, the risk increased with elevated plasma cotinine levels until 1199 nmol L^-1 (HR: 1.55, 95% CI: 1.16-2.05 at the third group vs. the reference group) and plateaued at higher levels.

CONCLUSIONS

Current, but not former smokers, had a higher risk of developing AF. Use of plasma cotinine measurement corroborated this finding.

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 (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.

Linac4 low energy beam measurements with negative hydrogen ions

Linac4, a 160 MeV normal-conducting H(-) linear accelerator, is the first step in the upgrade of the beam intensity available from the LHC proton injectors at CERN. The Linac4 Low Energy Beam Transport (LEBT) line from the pulsed 2 MHz RF driven ion source, to the 352 MHz RFQ (Radiofrequency Quadrupole) has been built and installed at a test stand, and has been used to transport and match to the RFQ a pulsed 14 mA H(-) beam at 45 keV. A temporary slit-and-grid emittance measurement system has been put in place to characterize the beam delivered to the RFQ. In this paper a description of the LEBT and its beam diagnostics is given, and the results of beam emittance measurements and beam transmission measurements through the RFQ are compared with the expectation from simulations.

Status and operation of the Linac4 ion source prototypes

CERN's Linac4 45 kV H(-) ion sources prototypes are installed at a dedicated ion source test stand and in the Linac4 tunnel. The operation of the pulsed hydrogen injection, RF sustained plasma, and pulsed high voltages are described. The first experimental results of two prototypes relying on 2 MHz RF-plasma heating are presented. The plasma is ignited via capacitive coupling, and sustained by inductive coupling. The light emitted from the plasma is collected by viewports pointing to the plasma chamber wall in the middle of the RF solenoid and to the plasma chamber axis. Preliminary measurements of optical emission spectroscopy and photometry of the plasma have been performed. The design of a cesiated ion source is presented. The volume source has produced a 45 keV H(-) beam of 16-22 mA which has successfully been used for the commissioning of the Low Energy Beam Transport (LEBT), Radio Frequency Quadrupole (RFQ) accelerator, and chopper of Linac4.

A community-based study on determinants of circulating markers of cellular immune activation and kynurenines: the Hordaland Health Study

Circulating neopterin and kynurenine/tryptophan ratio (KTR) increase during inflammation and serve as markers of cellular immune activation, but data are sparse on other determinants of these markers and metabolites of the kynurenine pathway. We measured neopterin, tryptophan, kynurenine, anthranilic acid, kynurenic acid, 3-hydroxykynurenine, 3-hydroxyanthranilic acid and xanthurenic acid in plasma in two age groups, 45-46 years (n = 3723) and 70-72 years (n = 3329). Differences across categories of the potential determinants, including age, gender, renal function, body mass index (BMI), smoking and physical activity, were tested by Mann-Whitney U-test and multiple linear regression including age group, gender, renal function and lifestyle factors. In this multivariate model, neopterin, KTR and most kynurenines were 20-30% higher in the older group, whereas tryptophan was 7% lower. Men had 6-19% higher concentrations of tryptophan and most kynurenines than women of the same age. Compared to the fourth age-specific estimated glomerular filtration rate (eGFR) quartile, the first quartile was associated with higher concentrations of neopterin (25%) and KTR (24%) and 18-36% higher concentrations of kynurenines, except 3-hydroxyanthranilic acid. Additionally, KTR, tryptophan and all kynurenines, except anthranilic acid, were 2-8% higher in overweight and 3-17% higher in obese, than in normal-weight individuals. Heavy smokers had 4-14% lower levels of tryptophan and most kynurenines than non-smokers. Age and renal function were the strongest determinants of plasma neopterin, KTR and most kynurenines. These findings are relevant for the design and interpretation of studies investigating the role of plasma neopterin, KTR and kynurenines in chronic diseases.

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.

A new extraction system for the Linac4 H- ion source

As part of the CERN accelerator complex upgrade, a new linear accelerator for H(-) (Linac4) is under construction. The ion source design is based on the non-caesiated DESY RF-driven ion source, with the goal of producing an H(-) beam of 80 mA beam current, 45 keV beam energy, 0.4 ms pulse length, and 2 Hz repetition rate. The source has been successfully commissioned for an extraction voltage of 35 kV, corresponding to the one used at DESY. Increasing the extraction voltage to 45 kV has resulted in frequent high voltage breakdowns in the extraction region caused by evaporating material from the electron dump, triggering a new design of the extraction and electron dumping system. Results of the ion source commissioning at 35 kV are presented as well as simulations of a new pulsed extraction system for beam extraction at 45 kV.

Combined analyses and extended follow-up of two randomized controlled homocysteine-lowering B-vitamin trials

OBJECTIVES

In the Norwegian Vitamin Trial and the Western Norway B Vitamin Intervention Trial, patients were randomly assigned to homocysteine-lowering B-vitamins or no such treatment. We investigated their effects on cardiovascular outcomes in the trial populations combined, during the trials and during an extended follow-up, and performed exploratory analyses to determine the usefulness of homocysteine as a predictor of cardiovascular outcomes.

DESIGN

Pooling of data from two randomized controlled trials (1998-2005) with extended post-trial observational follow-up until 1 January 2008.

SETTING

Thirty-six hospitals in Norway.

SUBJECTS

6837 patients with ischaemic heart disease.

INTERVENTIONS

One capsule per day containing folic acid (0.8 mg) plus vitamin B12 (0.4 mg) and vitamin B6 (40 mg), or folic acid plus vitamin B12, or vitamin B6 alone or placebo.

MAIN OUTCOME MEASURES

Major adverse cardiovascular events (MACEs; cardiovascular death, acute myocardial infarction or stroke) during the trials and cardiovascular mortality during the extended follow-up.

RESULTS

Folic acid plus vitamin B12 treatment lowered homocysteine levels by 25% but did not influence MACE incidence (hazard ratio, 1.07; 95% CI, 0.95-1.21) during 39 months of follow-up, or cardiovascular mortality (hazard ratio, 1.12; 95% CI, 0.95-1.31) during 78 months of follow-up, when compared to no such treatment. Baseline homocysteine level was not independently associated with study outcomes. However, homocysteine concentration measured after 1-2 months of folic acid plus vitamin B12 treatment was a strong predictor of MACEs.

CONCLUSION

We found no short- or long-term benefit of folic acid plus vitamin B12 on cardiovascular outcomes in patients with ischaemic heart disease. Our data suggest that cardiovascular risk prediction by plasma total homocysteine concentration may be confined to the homocysteine fraction that does not respond to B-vitamins.

Commissioning of the new H- source for Linac4

As part of the CERN accelerator complex upgrade, a new linear accelerator for H(-) (Linac4) will start its operation in 2014. The source for this linac will be a 2 MHz rf driven H(-) source which is a copy of the very successful source from DESY. In this paper the design and the first results of the commissioning are reported. The commissioning has progressed successfully, and no major obstacles have been identified which will prevent reaching the goal of 80 mA H(-) beam current, 45 keV beam energy, 0.4 ms pulse length, and 2 Hz repetition rate. The source is producing up until now a stable beam of 23 mA, 35 keV, and with a repetition rate of 0.83 Hz.

Multivariate Screening Analysis of Water-in-Oil Emulsions in High External Electric Fields as Studied by Means of Dielectric Time Domain Spectroscopy

The effect of crude oil resins with various polar characters on the stability of w/o model emulsions containing asphaltenes is investigated using a mixture design. The resins were extracted using an adsorption-desorption technique. One asphaltene fraction and four different resin fractions from one European crude oil were used. The stabilities are measured using time-domain dielectric spectroscopy in high external electric field. It is found that resins with different polar character have different effects on the emulsion stability. At asphaltene/resin ratios of 1 and 5 : 3 the resins in some cases lead to an emulsion stability higher than that of a similar emulsion stabilized by asphaltenes only, while at low asphaltene/resin ratios ( approximately 1 : 3) the emulsion stability is reduced by the resins. The effect on emulsion stability of combining two different resin fractions depended on the resin types combined as well as the relative amount of resins and asphaltenes. Also, an increase in the stability of some of the emulsions containing resins and asphaltenes for a period of 50-300 min after the emulsification was observed. This time-dependence of emulsion stability is attributed to the mobility of resins at the oil-water interface and the slow buildup of a stabilizing interfacial film consisting of resins and asphaltenes. Copyright 2000 Academic Press.