Temporal changes in postprandial blood transcriptomes reveal subject-specific pattern of expression of innate immunity genes after a high-fat meal

Single high-fat challenge and trained innate immunity: A randomized controlled cross-over trial

Brief exposure of monocytes to atherogenic molecules, such as oxidized lipoproteins, triggers a persistent pro-inflammatory phenotype, named trained immunity. In mice, transient high-fat diet leads to trained immunity, which aggravates atherogenesis. We hypothesized that a single high-fat challenge in humans induces trained immunity. In a randomized controlled cross-over study, 14 healthy individuals received a high-fat or reference shake, and blood was drawn before and after 1, 2, 4, 6, 24, and 72 h. Incubation of donor monocytes with the post-high-fat-shake serum induced trained immunity, regulated via Toll-like receptor 4. This was not mediated via triglyceride-rich lipoproteins, C12, 14, and 16, or metabolic endotoxemia. In vivo, however, the high-fat challenge did not affect monocyte phenotype and function. We conclude that a high-fat challenge leads to alterations in the serum composition that have the potential to induce trained immunity in vitro. However, this does not translate into a (persistent) hyperinflammatory monocyte phenotype in vivo.

Systematic Review and Quantitative Data Synthesis of Peripheral Blood Mononuclear Cell Transcriptomics Reveals Consensus Gene Expression Changes in Response to a High Fat Meal

SCOPE

Metabolic flexibility is essential for a healthy response to a high fat meal, and is assessed by measuring postprandial changes in blood markers including peripheral blood mononuclear cells (PBMCs; lymphocytes and monocytes). However, there is no clear consensus on postprandial gene expression and protein changes in these cells.

METHOD AND RESULTS

The study systematically reviews the literature reporting transcriptional and proteomic changes in PBMCs after consumption of a high fat meal. After re-analysis of the raw data to ensure equivalence between studies, ≈85 genes are significantly changed (defined as in the same direction in ≥3 studies) with about half involved in four processes: inflammation/oxidative stress, GTP metabolism, apoptosis, and lipid localization/transport. For meals consisting predominantly of unsaturated fatty acids (UFA), notable additional processes are phosphorylation and glucocorticoid response. For saturated fatty acids (SFA), genes related to migration/angiogenesis and platelet aggregation are also changed.

CONCLUSION

Despite differences in study design, common gene changes are identified in PBMCs following a high fat meal. These common genes and processes will facilitate definition of the postprandial transcriptome as part of the overall postcibalome, linking all molecules and processes that change in the blood after a meal.

Blueberries and their bioactives in the modulation of oxidative stress, inflammation and cardio/vascular function markers: a systematic review of human intervention studies

Blueberries represent a rich source of (poly)phenols and other bioactive compounds. Numerous in vitro and animal model studies documented the potential health-promoting properties of blueberries and blueberry-bioactives, while little is still known about their effects in humans. The objective of the present systematic review is to provide main evidence and the potential mechanisms of action of blueberry and its (poly)phenols in the regulation of markers related to oxidative stress, inflammation, vascular and cardiometabolic function in health and disease states. A total of 45 human intervention studies were included in this review. Overall, the evidence suggests that blueberries may play a role in the improvement of markers of vascular function. Their effects were observed following both post-prandial and long-term consumption, particularly in subjects with risk factors and/or disease conditions. Conversely, the conflicting results on inflammation, oxidative stress and cardiometabolic risk markers were most likely due to differences among studies in terms of study design, subject characteristics, duration of intervention, dosage, and type of biomarkers analyzed. For these reasons, high-quality, well-designed, human intervention studies are warranted to strengthen the current findings on vascular function and provide more evidence about the impact of blueberries on the different markers considered. In addition, studies focusing on the relationship between the structure and the function of (poly)phenols will be fundamental for a better comprehension of the mechanisms behind the health effects observed.

Peripheral blood RNA biomarkers for cardiovascular disease from bench to bedside: a position paper from the EU-CardioRNA COST action CA17129

Despite significant advances in the diagnosis and treatment of cardiovascular diseases, recent calls have emphasized the unmet need to improve precision-based approaches in cardiovascular disease. Although some studies provide preliminary evidence of the diagnostic and prognostic potential of circulating coding and non-coding RNAs, the complex RNA biology and lack of standardization have hampered the translation of these markers into clinical practice. In this position paper of the CardioRNA COST action CA17129, we provide recommendations to standardize the RNA development process in order to catalyse efforts to investigate novel RNAs for clinical use. We list the unmet clinical needs in cardiovascular disease, such as the identification of high-risk patients with ischaemic heart disease or heart failure who require more intensive therapies. The advantages and pitfalls of the different sample types, including RNAs from plasma, extracellular vesicles, and whole blood, are discussed in the sample matrix, together with their respective analytical methods. The effect of patient demographics and highly prevalent comorbidities, such as metabolic disorders, on the expression of the candidate RNA is presented and should be reported in biomarker studies. We discuss the statistical and regulatory aspects to translate a candidate RNA from a research use only assay to an in-vitro diagnostic test for clinical use. Optimal planning of this development track is required, with input from the researcher, statistician, industry, and regulatory partners.

Immune and hormonal regulation of the Boa constrictor (Serpentes; Boidae) in response to feeding

Feeding upregulates immune function and the systemic and local (gastrointestinal tract) concentrations of some immunoregulatory hormones, as corticosterone (CORT) and melatonin (MEL), in mammals and anurans. However, little is known about the immune and hormonal regulation in response to feeding in other ectothermic vertebrates, especially snakes, in which the postprandial metabolic changes are pronounced. Here, we investigated the effects feeding have on hormonal and innate immune responses in the snake, Boa constrictor. We divided juvenile males into two groups: fasting and fed with mice (30% of body mass). We measured the rates of oxygen consumption, plasma CORT levels, heterophil/lymphocyte ratio (HL ratio), plasma bacterial killing ability (BKA), and stomach and intestine MEL in fasting snakes and 48 h after meal intake. We observed increased rates of oxygen consumption, plasma CORT levels, and HL ratio, along with a tendency of decreased stomach and intestine MEL in fed snakes compared to fasting ones. BKA was not affected by feeding. Overall, we found that feeding modulates metabolic rates, CORT levels, and immune cell distribution in boas. Increased baseline CORT may be important to mobilize energy to support the metabolic increment during the postprandial period. Increased HL ratio might be an immunoregulatory effect of increased CORT, which has been shown in different physiological situations such as in response to immune challenge. Our results suggest that feeding activates the hypothalamic-pituitary-adrenal axis and modulates immune cell redistribution, possibly contributing to fighting potential injuries and infections derived from predation and from pathogens present in ingested food.

Immune and hormonal modulation in the postprandial period of bullfrogs (Lithobates catesbeianus)

Mammals show immune up-regulation and increased plasma and local (gastrointestinal tract) concentrations of some immunoregulatory hormones, such as corticosterone and melatonin, after feeding. However, little is known about the endocrine and immune modulation in the postprandial period of ectothermic animals. This study investigated the effects of feeding on endocrine and immune responses in the bullfrog (Lithobates catesbeianus). Frogs were fasted for 10 days and divided into two groups: fasted and fed with fish feed (5% of body mass). Blood and gastrointestinal tract tissues (stomach and intestine) were collected at 6, 24, 48, 96 and 168 h to measure neutrophil/lymphocyte ratio, plasma bacterial killing ability, phagocytosis of blood leukocytes, plasma corticosterone and melatonin, and stomach and intestine melatonin. Feeding increased plasma corticosterone at 24 h and decreased it at 168 h, and increased neutrophil/lymphocyte ratio at 6, 24 and 96 h. We also observed decreased bacterial killing ability 48 h after feeding. Stomach melatonin increased after 17 days of fasting. We show that feeding activates the hypothalamic-pituitary-interrenal axis and promotes transient immunosuppression, without stimulating an inflammatory response. Increased corticosterone may mobilize energy to support digestive processes and melatonin may protect the stomach during fasting. We conclude that feeding modulates secretion of immunoregulatory hormones, initially increasing plasma corticosterone levels, followed by a decrease at the end of meal digestion, and causes systemic immune cell redistribution, increasing neutrophil/lymphocyte ratio for almost the entire period of meal digestion in bullfrogs. Also, fasting modulates secretion of melatonin in the stomach.

Construction of Condition-Specific Gene Regulatory Network Using Kernel Canonical Correlation Analysis

Gene expression profile or transcriptome can represent cellular states, thus understanding gene regulation mechanisms can help understand how cells respond to external stress. Interaction between transcription factor (TF) and target gene (TG) is one of the representative regulatory mechanisms in cells. In this paper, we present a novel computational method to construct condition-specific transcriptional networks from transcriptome data. Regulatory interaction between TFs and TGs is very complex, specifically multiple-to-multiple relations. Experimental data from TF Chromatin Immunoprecipitation sequencing is useful but produces one-to-multiple relations between TF and TGs. On the other hand, co-expression networks of genes can be useful for constructing condition transcriptional networks, but there are many false positive relations in co-expression networks. In this paper, we propose a novel method to construct a condition-specific and combinatorial transcriptional network, applying kernel canonical correlation analysis (kernel CCA) to identify multiple-to-multiple TF-TG relations in certain biological condition. Kernel CCA is a well-established statistical method for computing the correlation of a group of features vs. another group of features. We, therefore, employed kernel CCA to embed TFs and TGs into a new space where the correlation of TFs and TGs are reflected. To demonstrate the usefulness of our network construction method, we used the blood transcriptome data for the investigation on the response to high fat diet in a human and an arabidopsis data set for the investigation on the response to cold/heat stress. Our method detected not only important regulatory interactions reported in previous studies but also novel TF-TG relations where a module of TF is regulating a module of TGs upon specific stress.

Endotoxin May Not Be the Major Cause of Postprandial Inflammation in Adults Who Consume a Single High-Fat or Moderately High-Fat Meal

BACKGROUND

Metabolic endotoxemia is considered a cause for high-fat diet (HFD)-induced inflammation. However, convincing experimental evidence in humans is scant.

OBJECTIVE

We determined whether a HFD or moderately HFD increases LPS and LPS-mediated cytokine production in the postprandial blood (PPB).

METHODS

Ninety-eight volunteers (age: 37.3 ± 1.5 y) from the cross-sectional phenotyping study (PS) and 62 volunteers (age: 26.8 ± 1.2 y) from the intervention study (IS) consumed a breakfast containing 60% kcal fat (HF) and 36% kcal fat (moderately HF), respectively. For the IS, only the results from the placebo group are presented. Blood samples were probed for LPS-mediated cytokine production by incubating them with LPS inhibitor polymyxin B (PMB) for 24 h at 37°C besides the Limulus amebocyte lysate (LAL) assay. Repeated-measures ANOVA was used to compare the temporal changes of metabolic profiles and treatment outcomes.

RESULTS

At least 87.5% of the plasma LPS measurements in 32 PS volunteers from each time point were below the LAL assay sensitivity (0.002 EU/mL). PMB suppressed IL-1β (P = 0.035) and IL-6 (P = 0.0487) production in the 3 h PPB of the PS after 24 h incubation at 37°C compared to the vehicle control, suggesting the presence of LPS. However, the amount of LPS did not increase the cytokine concentrations in the 3 h PPB above the fasting concentrations. Such suppression was not detected in the PPB of the IS. Treating whole blood with lipoprotein lipase (LPL) significantly (P < 0.05) increased FFA and cytokine (IL-1β, IL-6, TNF-α) concentrations in both studies.

CONCLUSION

LPS may not be the major cause of postprandial inflammation in healthy adults consuming a moderately HF meal (36% kcal fat, similar to the typical American diet) or a HF meal (60% kcal fat). Plasma FFAs may modulate postprandial inflammation. The prevailing concept of HFD-induced metabolic endotoxemia requires careful re-evaluation. The PS was registered at clinicaltrials.gov as NCT02367287 and the IS as NCT02472171.