Biomarkers of one-carbon metabolism and B-vitamin status : Targeted metabolomics in rats and humans exploring the effects of PPARα-activation and dietary composition

BACKGROUND: One-carbon metabolism is an overarching term describing central metabolic pathways involved in the transfer of one-carbon units. These include the methionine-homocysteine and folate cycles, as well as the choline oxidation and transsulfuration pathways, all of which depend on B-vitamins as cofactors. Circulating concentrations of several metabolites and intermediates of these metabolic pathways have been linked to chronic disease risk. Thus, extending our knowledge regarding the regulation of these pathways is warranted. Targeted metabolomics offers the opportunity to study the concentration of several metabolites of these pathways simultaneously, and is thus required for the thorough investigation of the effects of diet and other factors on one-carbon metabolism. Diet provides both substrates, cofactors and one-carbon units, influencing the complex regulation of the different metabolic pathways. Furthermore, of particular interest is the activation of the nuclear receptor PPAR (peroxisome proliferator-activated receptor) α, a lipid sensor involved in the regulation of energy metabolism. The overall aim of this thesis was to utilize targeted metabolomics to explore the effect of PPARα-activation and dietary composition on of one-carbon metabolism and B-vitamin status. The effect of pharmacological PPARα-activation was addressed in Paper I and II, taking advantage of studies in laboratory animals. In Paper III, the effect of dietary macronutrient composition was investigated in a cross-sectional analysis of a human cohort. METHODS: Animal models: We utilized data from two animal experiments, where male Wistar rats were treated with PPAR-agonists. In the first experiment, the rats received a pan-PPAR-agonist for 50 weeks. In the second experiment, specific PPARα and γ- agonists were administered for 12 days. In both studies, plasma concentrations of metabolites were compared between treated and control animals. Human study: This was a cross-sectional analysis in a cohort of 1928 patients with stable angina pectoris. Dietary data was derived from a food frequency questionnaire, and associations between dietary composition and plasma metabolite concentrations were assessed with multiple linear regression analyses. In all studies, plasma one carbon metabolites and B-vitamin markers were quantified by applying mass spectrometric methods. RESULTS: Long-term (Paper I) and short-term (Paper II) pharmacological PPARα-activation influenced the one-carbon metabolome, with the strongest effects seen for increased plasma concentration of nicotinamide and methylnicotinamide (vitamin B3), pyridoxal (vitamin B6), methylmalonic acid (marker of vitamin B12 status), dimethylglycine and glycine (choline oxidation pathway metabolites), and reduced flavin mononucleotide (vitamin B2). In humans, the observed effects of macronutrient intake were strongest for protein, where increased intake was associated with higher plasma concentrations of pyridoxal, pyridixal-5-phosphate and pyridoxic acid (vitamin B6), vitamin B12, riboflavin (vitamin B2) and methylnicotinamide. Further, we observed inverse associations between protein intake and plasma homocysteine and methylmalonic acid concentrations. When modeling the substitution of saturated with polyunsaturated fatty acids, we observed higher methylnicotinamide, pyridoxal, pyridixal-5-phosphate, cobalamin and dimethylglycine, as well as lower riboflavin concentrations. CONCLUSION AND IMPLICATION: PPARα-activation and dietary macronutrient composition altered the concentration of circulating biomarkers of one carbon metabolism. The effects of PPARα-activation were consistent across different conditions, and our results strongly suggest a central role for PPARα in the regulation of these metabolic pathways. Estimated effects of substituting saturated with polyunsaturated fatty acids yielded associations with the biomarkers similar to those observed with PPARα-activation in the animal studies. This suggests that the effects of diet on one-carbon metabolism, especially related to dietary fatty acid composition, may be partly mediated through altered PPARα-activity. This is the first metabolomic investigation targeting the majority of the metabolites of the one-carbon metabolism pathways simultaneously. Linking mechanistic studies in animals with observational data in humans provides novel information regarding metabolic regulations. The current investigations extend our understanding of how PPARα-activation and dietary composition influences the one-carbon metabolome. Application to the human situation will offer potential for more individualized dietary advice

No effect of plasma trimethylamine N-Oxide (TMAO) and plasma trimethyllysine (TML) on the association between choline intake and acute myocardial infarction risk in patients with stable angina pectoris

Plasma concentrations of trimethylamine N-oxide (TMAO) have been linked to cardiovascular disease (CVD) risk and mortality. TMAO is formed through the bacterial conversion of trimethylamine which is obtained either directly from food, generated from dietary precursors (e.g. choline) or derived from endogenous trimethyllysine (TML) production. In a previous article, we reported an increased risk of acute myocardial infarction with increased total choline intake in patients with stable angina pectoris. Due to the close link between TMAO, TML, choline metabolism and possibly CVD, we investigated whether plasma TMAO and TML modified the effect of total choline intake on acute myocardial infarction (AMI) risk in a post-hoc analysis. We found plasma TMAO and TML do not modify the association between higher dietary choline intake and increased AMI risk. Additionally, this association is not mediated via TMAO.publishedVersio

MRI adipose tissue segmentation and quantification in R (RAdipoSeg)

Background: Excess adipose tissue is associated with increased cardiovascular and metabolic risk, but the volume of visceral and subcutaneous adipose tissue poses different metabolic risks. MRI with fat suppression can be used to accurately quantify adipose depots. We have developed a new semi-automatic method, RAdipoSeg, for MRI adipose tissue segmentation and quantification in the free and open source statistical software R. Methods: MRI images were obtained from wild-type mice on high- or low-fat diet, and from 20 human subjects without clinical signs of metabolic dysfunction. For each mouse and human subject, respectively, 10 images were segmented with RAdipoSeg and with the commercially available software SliceOmatic. Jaccard difference, relative volume difference and Spearman’s rank correlation coefficients were calculated for each group. Agreement between the two methods were analysed with Bland–Altman plots. Results: RAdipoSeg performed similarly to the commercial software. The mean Jaccard differences were 10–29% and the relative volume differences were below ( ±) 20%. Spearman’s rank correlation coefficient gave p-values below 0.05 for both mouse and human images. The Bland–Altman plots indicated some systematic and proporitional bias, which can be countered by the flexible nature of the method. Conclusion: RAdipoSeg is a reliable and low cost method for fat segmentation in studies of mice and humans.publishedVersio

Food Sources Contributing to Intake of Choline and Individual Choline Forms in a Norwegian Cohort of Patients With Stable Angina Pectoris

Choline is an essential nutrient involved in a wide range of physiological functions. It occurs in water- and lipid-soluble forms in the body and diet. Foods with a known high choline content are eggs, beef, chicken, milk, fish, and selected plant foods. An adequate intake has been set in the US and Europe, however, not yet in the Nordic countries. A higher intake of lipid-soluble choline forms has been associated with increased risk of acute myocardial infarction, highlighting the need for knowledge about food sources of the individual choline forms. In general, little is known about the habitual intake and food sources of choline, and individual choline forms.publishedVersio

Short-term activation of peroxisome proliferator-activated receptors α and γ induces tissue-specific effects on lipid metabolism and fatty acid composition in male Wistar rats

Dietary fatty acids (FAs) affect certain metabolic routes, including pathways controlled by the peroxisome proliferator-activated receptors (PPARs), but tissue-specific effects are not well-defined. Thus, the aim was to compare the metabolic response in hepatic, adipose, and cardiac tissues after treatment with specific PPAR agonists. Male Wistar rats were randomized into three groups: a control group receiving placebo (n=8); a PPARα agonist group receiving WY-14,643 (n=6); and a PPARγ agonist group receiving rosiglitazone (n=6) for 12 days. All animals received a low-fat standard chow diet and were given a daily dose of placebo or agonist orally. Lipids and FA methyl esters were measured in plasma, liver, and heart and gene expression was measured in liver and adipose tissue, while enzyme activities were measured in liver. Treatment with the PPARα agonist was associated with higher liver mass relative to body weight (liver index), lower plasma, and hepatic total cholesterol, as well as lower plasma carnitine and acylcarnitines, compared with control. In heart, PPARα activation leads to overall lower levels of free FAs and specific changes in certain FAs, compared with control. Furthermore, β-oxidation in liver and the enzymatic activities of well-known PPARα targeted genes were higher following PPARα administration. Overall, rats treated with the PPARα agonist had higher hepatic saturated FAs (SFAs) and monounsaturated FAs (MUFAs) and lower n-6 and n-3 PUFAs, compared to control. Treatment with the PPARγ agonist was associated with a lower liver index, lower plasma triglycerides (TAG) and phospholipids, and higher hepatic phospholipids, compared with control. PPARγ target genes were increased specifically in adipose tissue. Moreover, lower total cardiac FAs and SFA and higher cardiac n-6 PUFA were also associated with PPARγ activation. Altogether, there were characteristic effects of PPARα activation in liver and heart, as well as in plasma. PPARγ effects were not only confined to adipose tissue, but specific effects were also seen in liver, heart, and plasma. In conclusion, short-term treatment with PPAR agonists induced tissue-specific effects on FA composition in liver and heart. Moreover, both PPARα and PPARγ activation lowered plasma TAG and phospholipids, most likely through effects on liver and adipose tissue, respectively. In future studies we aim to reveal whether similar patterns can be found through diet-induced activation of specific pathways.publishedVersio

Association of dietary vitamin K and risk of coronary heart disease in middle-age adults: the Hordaland Health Study Cohort

Objective: The role of vitamin K in the regulation of vascular calcification is established. However, the association of dietary vitamins K1 and K2 with risk of coronary heart disease (CHD) is inconclusive. Design: Prospective cohort study. Setting: We followed participants in the community-based Hordaland Health Study from 1997 - 1999 through 2009 to evaluate associations between intake of vitamin K and incident (new onset) CHD. Baseline diet was assessed by a past-year food frequency questionnaire. Energy-adjusted residuals of vitamin K1 and vitamin K2 intakes were categorised into quartiles. Participants: 2987 Norwegian men and women, age 46–49 years. Methods: Information on incident CHD events was obtained from the nationwide Cardiovascular Disease in Norway (CVDNOR) Project. Multivariable Cox regression estimated HRs and 95% CIs with test for linear trends across quartiles. Analyses were adjusted for age, sex, total energy intake, physical activity, smoking and education. A third model further adjusted K1 intake for energy-adjusted fibre and folate, while K2 intake was adjusted for energy-adjusted saturated fatty acids and calcium. Results: During a median follow-up time of 11 years, we documented 112 incident CHD cases. In the adjusted analyses, there was no association between intake of vitamin K1 and CHD (HRQ4vsQ1 = 0.92 (95% CI 0.54 to 1.57), p for trend 0.64), while there was a lower risk of CHD associated with higher intake of energy-adjusted vitamin K2 (HRQ4vsQ1 = 0.52 (0.29 to 0.94), p for trend 0.03). Further adjustment for potential dietary confounders did not materially change the association for K1, while the association for K2 was slightly attenuated (HRQ4vsQ1 = 0.58 (0.28 to 1.19)). Conclusions: A higher intake of vitamin K2 was associated with lower risk of CHD, while there was no association between intake of vitamin K1 and CHD.publishedVersio

The Association of Meat Intake With All-Cause Mortality and Acute Myocardial Infarction Is Age-Dependent in Patients With Stable Angina Pectoris

Background: Red and processed meat intake have been associated with increased risk of morbidity and mortality, and a restricted intake is encouraged in patients with cardiovascular disease. However, evidence on the association between total meat intake and clinical outcomes in this patient group is lacking. Objectives: To investigate the association between total meat intake and risk of all-cause mortality, acute myocardial infarction, cancer, and gastrointestinal cancer in patients with stable angina pectoris. We also investigated whether age modified these associations. Materials and Methods: This prospective cohort study consisted of 1,929 patients (80% male, mean age 62 years) with stable angina pectoris from the Western Norway B-Vitamin Intervention Trial. Dietary assessment was performed by the administration of a semi-quantitative food frequency questionnaire. Cox proportional hazards models were used to investigate the association between a relative increase in total meat intake and the outcomes of interest. Results: The association per 50 g/1,000 kcal higher intake of total meat with morbidity and mortality were generally inconclusive but indicated an increased risk of acute myocardial infarction [HR: 1.26 (95% CI: 0.98, 1.61)] and gastrointestinal cancer [1.23 (0.70, 2.16)]. However, we observed a clear effect modification by age, where total meat intake was associated with an increased risk of mortality and acute myocardial infarction among younger individuals, but an attenuation, and even reversal of the risk association with increasing age. Conclusion: Our findings support the current dietary guidelines emphasizing a restricted meat intake in cardiovascular disease patients but highlights the need for further research on the association between meat intake and health outcomes in elderly populations. Future studies should investigate different types of meat separately in other CVD-cohorts, in different age-groups, as well as in the general population.publishedVersio

Exploratory analyses on the effect of time since last meal on concentrations of amino acids, lipids, one-carbon metabolites, and vitamins in the Hordaland Health Study

Purpose Dietary intake may have pronounced effects on circulating biomarker concentrations. Therefore, the aim was to provide a descriptive overview of serum metabolite concentrations in relation to time since last meal, focusing on amino acids, lipids, one-carbon metabolites, and biomarkers of vitamin status. Methods We used baseline data from the observational community-based Hordaland Health Study, including 2960 participants aged 46–49 years and 2874 participants aged 70–74 years. A single blood draw was taken from each participant, and time since last meal varied. Estimated marginal geometric mean metabolite concentrations were plotted as a function of time since last meal, up to 7 h, adjusted for age, sex, and BMI. Results We observed a common pattern for nearly all amino acids and one-carbon metabolites with highest concentrations during the first 3 h after dietary intake. Homocysteine and cysteine were lowest the 1st hour after a meal, while no patterns were observed for glutamate and glutamic acid. The concentrations of phylloquinone and triglycerides were highest 1 h after dietary intake. Thiamine and thiamine monophosphate concentrations were highest, while flavin mononucleotide concentrations were lowest within the first 2 h after a meal. No clear patterns emerged for the other fat-soluble vitamins, blood lipids, or B-vitamin biomarkers. Conclusion Our findings suggest that distinguishing between “fasting” and “non-fasting” blood samples may be inadequate, and a more granular approach is warranted. This may have implications for how to account for dietary intake when blood sampling in both clinical and research settings.publishedVersio

Primary cardiovascular risk prediction by LDL-cholesterol in Caucasian middle-aged and older adults: a joint analysis of three cohorts

Under embargo until: 2022-06-01Aims Low-density lipoprotein cholesterol (LDL-C) is an established causal driver of atherosclerotic cardiovascular disease (ASCVD), but its performance and age-dependency as a biomarker for incident events and mortality arising from ASCVD is less clear. The aim was to determine the value of LDL-C as a susceptibility/risk biomarker for incident coronary heart disease (CHD), ASCVD, and stroke events and deaths, for the age groups <50 and ≥50 years. Methods and results The performance of LDL-C was evaluated in three cohorts, FINRISK 2002 (n = 7709), HUSK (n = 5431), and ESTHER (n = 4559), by Cox proportional hazards models, C-statistics, and net reclassification index calculations. Additionally, the hazard ratios (HRs) for the three cohorts were pooled by meta-analysis. The most consistent association was observed for CHD [95% confidence interval (CI) for HRs per standard deviation ranging from 0.99 to 1.37], whereas the results were more modest for ASCVD (0.96–1.18) due to lack of association with stroke (0.77–1.24). The association and discriminatory value of LDL-C with all endpoints in FINRISK 2002 and HUSK were attenuated in subjects 50 years and older [HRs (95% CI) obtained from meta-analysis 1.11 (1.04–1.18) for CHD, 1.15 (1.02–1.29) for CHD death, 1.02 (0.98–1.06) for ASCVD, 1.12 (1.02–1.23) for ASCVD death, and 0.97 (0.89–1.05) for stroke]. Conclusion In middle-aged and older adults, associations between LDL-C and all the studied cardiovascular endpoints were relatively weak, while LDL-C showed stronger association with rare events of pre-mature CHD or ASCVD death among middle-aged adults. The predictive performance of LDL-C also depends on the studied cardiovascular endpoint.acceptedVersio

Expanding the Utilization of Formalin-Fixed, Paraffin-Embedded Archives : Feasibility of miR-Seq for Disease Exploration and Biomarker Development from Biopsies with Clear Cell Renal Cell Carcinoma

Novel predictive tools for clear cell renal cell carcinoma (ccRCC) are urgently needed. MicroRNAs (miRNAs) have been increasingly investigated for their predictive value, and formalin-fixed paraffin-embedded biopsy archives may potentially be a valuable source of miRNA sequencing material, as they remain an underused resource. Core biopsies of both cancerous and adjacent normal tissues were obtained from patients (n = 12) undergoing nephrectomy. After small RNA-seq, several analyses were performed, including classifier evaluation, obesity-related inquiries, survival analysis using publicly available datasets, comparisons to the current literature and ingenuity pathway analyses. In a comparison of tumour vs. normal, 182 miRNAs were found with significant differential expression; miR-155 was of particular interest as it classified all ccRCC samples correctly and correlated well with tumour size (R-2 = 0.83); miR-155 also predicted poor survival with hazard ratios of 2.58 and 1.81 in two different TCGA (The Cancer Genome Atlas) datasets in a univariate model. However, in a multivariate Cox regression analysis including age, sex, cancer stage and histological grade, miR-155 was not a statistically significant survival predictor. In conclusion, formalin-fixed paraffin-embedded biopsy tissues are a viable source of miRNA-sequencing material. Our results further support a role for miR-155 as a promising cancer classifier and potentially as a therapeutic target in ccRCC that merits further investigation.Peer reviewe