Ethnic differences in postprandial fatty acid trafficking and utilization between overweight and obese White European and Black African-Caribbean men.

Black African-Caribbean (BAC) populations are at greater risk of cardiometabolic disease than White Europeans (WE), despite exhibiting lower fasting triacylglycerol (TAG) concentrations. However, limited data exist regarding postprandial fatty acid metabolism in BAC populations. This study determined the ethnic differences in postprandial fatty acid metabolism between overweight and obese WE and BAC men. WE [n = 10, age 33.3 ± 1.7 yr; body mass index (BMI) = 26.8 (25.8-31.0) kg/m2] and BAC [n = 9, age 27.9 ± 1.0 yr; BMI = 27.5 (26.0-28.6) kg/m2] men consumed two consecutive (at 0 and 300 min) moderate-to-high-fat meals-the first labeled with [U-13C]palmitate. The plasma concentration and appearance of meal-derived fatty acids in very-low-density lipoprotein (VLDL)-TAG, chylomicron-TAG, and nonesterified fatty acid (NEFA) were determined over an 8-h postprandial period. Indirect calorimetry with 13CO2 enrichment determined total and meal-derived fatty acid oxidation rates, and plasma ß-hydroxybutyrate (3-OHB) concentration was measured to assess ketogenesis. BAC exhibited lower postprandial TAG [area under the curve (AUC0-480) = 671 (563-802) vs. 469 (354-623) mmol/L/min, P = 0.022] and VLDL-TAG [AUC0-480 = 288 ± 30 vs. 145 ± 27 mmol/L/min, P = 0.003] concentrations than WE. The appearance of meal-derived fatty acids in VLDL-TAG was lower in BAC than in WE (AUC0-480 = 133 ± 12 vs. 78 ± 13 mmol/L/min, P = 0.007). Following the second meal, BAC showed a trend for lower chylomicron-TAG concentration [AUC300-480 = 69 (51-93) vs. 43 (28-67) mmol/L/min, P = 0.057]. There were no ethnic differences in the appearance of chylomicron-TAG, cumulative fatty acid oxidation, and the NEFA:3-OHB ratio (P > 0.05). In conclusion, BAC exhibit lower postprandial TAG concentrations compared with WE men, driven by lower VLDL-TAG concentrations and possibly lower chylomicron-TAG in the late postprandial period. These findings suggest that postprandial fatty acid trafficking may be a less important determinant of cardiometabolic risk in BAC than in WE men.NEW & NOTEWORTHY Postprandial TAG is lower in Black African-Caribbean men than in White European men, and this is likely driven by lower meal-derived VLDL-TAG in Black African-Caribbean men. This observation could suggest that fatty acid trafficking may be a less important determinant of cardiometabolic risk in Black Africans than in White European men.

Impact of a food-based dietary fat exchange model for replacing dietary saturated with unsaturated fatty acids in healthy men on plasma phospholipids fatty acid profiles and dietary patterns.

PURPOSE: UK guidelines recommend dietary saturated fatty acids (SFAs) should not exceed 10% total energy (%TE) for cardiovascular disease prevention, with benefits observed when SFAs are replaced with unsaturated fatty acids (UFAs). This study aimed to assess the efficacy of a dietary exchange model using commercially available foods to replace SFAs with UFAs. METHODS: Healthy men (n = 109, age 48, SD 11 year) recruited to the Reading, Imperial, Surrey, Saturated fat Cholesterol Intervention-1 (RISSCI-1) study (ClinicalTrials.Gov n°NCT03270527) followed two sequential 4-week isoenergetic moderate-fat (34%TE) diets: high-SFA (18%TE SFAs, 16%TE UFAs) and low-SFA (10%TE SFAs, 24%TE UFAs). Dietary intakes were assessed using 4-day weighed diet diaries. Nutrient intakes were analysed using paired t-tests, fasting plasma phospholipid fatty acid (PL-FA) profiles and dietary patterns were analysed using orthogonal partial least square discriminant analyses. RESULTS: Participants exchanged 10.2%TE (SD 4.1) SFAs for 9.7%TE (SD 3.9) UFAs between the high and low-SFA diets, reaching target intakes with minimal effect on other nutrients or energy intakes. Analyses of dietary patterns confirmed successful incorporation of recommended foods from commercially available sources (e.g. dairy products, snacks, oils, and fats), without affecting participants' overall dietary intakes. Analyses of plasma PL-FAs indicated good compliance to the dietary intervention and foods of varying SFA content. CONCLUSIONS: RISSCI-1 dietary exchange model successfully replaced dietary SFAs with UFAs in free-living healthy men using commercially available foods, and without altering their dietary patterns. Further intervention studies are required to confirm utility and feasibility of such food-based dietary fat replacement models at a population level.

Probiotic supplementation increases carbohydrate metabolism in trained male cyclists: a randomized, double-blind, placebo-controlled crossover trial.

We hypothesized that probiotic supplementation (PRO) increases the absorption and oxidation of orally ingested maltodextrin during 2 h endurance cycling, thereby sparing muscle glycogen for a subsequent time trial (simulating a road race). Measurements were made of lipid and carbohydrate oxidation, plasma metabolites and insulin, gastrointestinal (GI) permeability, and subjective symptoms of discomfort. Seven male cyclists were randomized to PRO (bacterial composition given in methods) or placebo for 4 wk, separated by a 14-day washout period. After each period, cyclists consumed a 10% maltodextrin solution (initial 8 mL/kg bolus and 2 mL/kg every 15 min) while exercising for 2 h at 55% maximal aerobic power output, followed by a 100-kJ time trial. PRO resulted in small increases in peak oxidation rates of the ingested maltodextrin (0.84 ± 0.10 vs. 0.77 ± 0.09 g/min; P = 0.016) and mean total carbohydrate oxidation (2.20 ± 0.25 vs. 1.87 ± 0.39 g/min; P = 0.038), whereas fat oxidation was reduced (0.40 ± 0.11 vs. 0.55 ± 0.10 g/min; P = 0.021). During PRO, small but significant increases were seen in glucose absorption, plasma glucose, and insulin concentration and decreases in nonesterified fatty acid and glycerol. Differences between markers of GI damage and permeability and time-trial performance were not significant (P > 0.05). In contrast to the hypothesis, PRO led to minimal increases in absorption and oxidation of the ingested maltodextrin and small reductions in fat oxidation, whereas having no effect on subsequent time-trial performance.

Transcriptomic analysis of human primary breast cancer identifies fatty acid oxidation as a target for metformin.

BACKGROUND: Epidemiological studies suggest that metformin may reduce the incidence of cancer in patients with diabetes and multiple late phase clinical trials assessing the potential of repurposing this drug are underway. Transcriptomic profiling of tumour samples is an excellent tool to understand drug bioactivity, identify candidate biomarkers and assess for mechanisms of resistance to therapy. METHODS: Thirty-six patients with untreated primary breast cancer were recruited to a window study and transcriptomic profiling of tumour samples carried out before and after metformin treatment. RESULTS: Multiple genes that regulate fatty acid oxidation were upregulated at the transcriptomic level and there was a differential change in expression between two previously identified cohorts of patients with distinct metabolic responses. Increase in expression of a mitochondrial fatty oxidation gene composite signature correlated with change in a proliferation gene signature. In vitro assays showed that, in contrast to previous studies in models of normal cells, metformin reduces fatty acid oxidation with a subsequent accumulation of intracellular triglyceride, independent of AMPK activation. CONCLUSIONS: We propose that metformin at clinical doses targets fatty acid oxidation in cancer cells with implications for patient selection and drug combinations. CLINICAL TRIAL REGISTRATION: NCT01266486.

Ω-3 index as a prognosis tool in cardiovascular disease.

PURPOSE OF REVIEW: In 2004, the 'Ω-3 index' was described as the sum of eicosapentaenoic acid (EPA, 20 : 5 n-3) and docosahexaenoic acid (DHA, 22 : 6 n-3) in red blood cells (RBCs) as an index of coronary heart disease mortality. This review outlines new evidence to support the Ω-3 index as a tool to inform disease prognosis. RECENT FINDINGS: Recent studies have reported differential metabolism of EPA and DHA. High-dose supplementation with EPA and DHA led to increased levels of RBC DHA that were associated with decreased liver fat. EPA and DHA in RBCs were associated with reduced mortality in a prospective study of patients with cardiac disease; the strongest association was with EPA. A diet containing 9.5-g α-linolenic acid lead to an increase in EPA but not DHA status in middle-aged women. SUMMARY: Dietary intake or supplementation studies with n-3 fatty acids should include measurement of n-3 status in a standardized way. The Ω-3 index, reflecting EPA and DHA status throughout the body, is convenient and may be appropriate in some cases, but as EPA and DHA assimilate differently in membranes, and have different potency, measurement of individual fatty acid composition in RBCs may be more informative.

Triglyceride-rich lipoprotein metabolism in women: roles of apoC-II and apoC-III.

BACKGROUND: Experimental data suggest that apolipoprotein (apo) C-II and C-III regulate triglyceride-rich lipoprotein (TRL) metabolism, but there are limited studies in humans. We investigated the metabolic associations of TRLs with apoC-II and apoC-III concentrations and kinetics in women. MATERIAL AND METHODS: The kinetics of plasma apoC-II, apoC-III and very low-density lipoprotein (VLDL) apoB-100 and triglycerides were measured in the postabsorptive state using stable isotopic techniques and compartmental modelling in 60 women with wide-ranging body mass index (19·5-32·9 kg/m(2) ). RESULTS: Plasma apoC-II and apoC-III concentrations were positively associated with the concentrations of plasma triglycerides, VLDL1 - and VLDL2 -apoB-100 and triglyceride (all P < 0·05). ApoC-II production rate (PR) was positively associated with VLDL1 -apoB-100 concentration, VLDL1 triglyceride concentration and VLDL1 triglyceride PR, while apoC-II fractional catabolic rate (FCR) was positively associated with VLDL1 triglyceride FCR (all P < 0·05). No significant associations were observed between apoC-II and VLDL2 apoB-100 or triglyceride kinetics. ApoC-III PR, but not FCR, was positively associated with VLDL1 triglyceride, and VLDL2 -apoB-100 and triglyceride concentrations (all P < 0·05). No significant associations were observed between apoC-III and VLDL-apoB-100 and triglyceride kinetics. In multivariable analysis, including homoeostasis model assessment score, menopausal status and obesity, apoC-II concentration was significantly associated with plasma triglyceride, VLDL1 -apoB-100 and VLDL1 triglyceride concentrations and PR. Using the same multivariable analysis, apoC-III was significantly associated with plasma triglyceride and VLDL1 - and VLDL2 -apoB-100 and triglyceride concentrations and FCR. CONCLUSIONS: In women, plasma apoC-II and apoC-III concentrations are regulated by their respective PR and are significant, independent determinants of the kinetics and plasma concentrations of TRLs.

Sugar and metabolic health: is there still a debate?

PURPOSE OF REVIEW: There is considerable political and public awareness of new recommendations to reduce sugars and sugar-sweetened beverages in our diets. It is therefore timely to review the most recent changes in guidelines, with a focus on evidence for metabolic health, recent research in the area and gaps in our knowledge. RECENT FINDINGS: Sufficient evidence links a high intake of sugar to dental caries and obesity, and high intakes of sugar-sweetened beverages in particular to increased risk of type 2 diabetes. This has led to the updating of dietary recommendations related to added sugars in the diet. The effects of specific sugars at usual intakes as part of an isoenergetic diet are less clear. The glycaemic response to food is complex and mediated by many factors, but sugar intake is not necessarily the major component. SUMMARY: There are many challenges faced by healthcare professionals and government bodies in order to improve the health of individuals and nations through evidence-based diets. Sufficiently powered long-term mechanistic studies are still required to provide evidence for the effects of reducing dietary sugars on metabolic health. However, there are many challenges for research scientists in the implementation of these studies.

Enhanced fatty acid uptake in visceral adipose tissue is not reversed by weight loss in obese individuals with the metabolic syndrome.

AIMS/HYPOTHESIS: Obesity causes an imbalance in fat mass distribution between visceral and subcutaneous adipose tissue (AT) depots. We tested the hypothesis that this relates to increased NEFA uptake between these depots in obese compared with healthy participants. Second, we hypothesised that a diet very low in energy (very low calorie diet [VLCD]) decreases fat mass in obese participants and that this is associated with the decline in NEFA uptake. METHODS: NEFA uptake in AT depots was measured with [(18)F]-fluoro-6-thia-heptadecanoic acid ((18)F-FTHA) and positron emission tomography (PET) in 18 obese participants with the metabolic syndrome before and after a 6 week VLCD. Whole body fat oxidation was measured using indirect calorimetry and [U-(13)C]palmitate. Sixteen non-obese participants were controls. RESULTS: Obese participants had >100% higher (p < 0.0001) NEFA uptake in the visceral and subcutaneous abdominal AT depots than controls. VLCD decreased AT mass in all regions (12% to 21%), but NEFA uptake was decreased significantly (18%; p < 0.006) only in the femoral AT. Whole body carbohydrate oxidation decreased, while fat oxidation increased. CONCLUSIONS/INTERPRETATION: The data demonstrate that weight loss caused by VLCD does not affect abdominal fasting NEFA uptake rates. We found that visceral fat takes up more NEFAs than subcutaneous AT depots, even after weight loss.

Fatty acid-binding protein 4, a point of convergence for angiogenic and metabolic signaling pathways in endothelial cells.

Fatty acid-binding protein 4 (FABP4) is an adipogenic protein and is implicated in atherosclerosis, insulin resistance, and cancer. In endothelial cells, FABP4 is induced by VEGFA, and inhibition of FABP4 blocks most of the VEGFA effects. We investigated the DLL4-NOTCH-dependent regulation of FABP4 in human umbilical vein endothelial cells by gene/protein expression and interaction analyses following inhibitor treatment and RNA interference. We found that FABP4 is directly induced by NOTCH. Stimulation of NOTCH signaling with human recombinant DLL4 led to FABP4 induction, independently of VEGFA. FABP4 induction by VEGFA was reduced by blockade of DLL4 binding to NOTCH or inhibition of NOTCH signal transduction. Chromatin immunoprecipitation of the NOTCH intracellular domain showed increased binding to two specific regions in the FABP4 promoter. The induction of FABP4 gene expression was dependent on the transcription factor FOXO1, which was essential for basal expression of FABP4, and FABP4 up-regulation following stimulation of the VEGFA and/or the NOTCH pathway. Thus, we show that the DLL4-NOTCH pathway mediates endothelial FABP4 expression. This indicates that induction of the angiogenesis-restricting DLL4-NOTCH can have pro-angiogenic effects via this pathway. It also provides a link between DLL4-NOTCH and FOXO1-mediated regulation of endothelial gene transcription, and it shows that DLL4-NOTCH is a nodal point in the integration of pro-angiogenic and metabolic signaling in endothelial cells. This may be crucial for angiogenesis in the tumor environment.

Variation of LDL cholesterol in response to the replacement of saturated with unsaturated fatty acids: a nonrandomized, sequential dietary intervention; the Reading, Imperial, Surrey, Saturated fat Cholesterol Intervention ("RISSCI"-1) study.

BACKGROUND: Serum low density lipoprotein (LDL) cholesterol shows marked interindividual variation in response to the replacement of saturated fatty acids (SFAs) with unsaturated fatty acids (UFAs). OBJECTIVES: To demonstrate the efficacy of United Kingdom guidelines for exchanging dietary SFAs for UFAs, to reduce serum LDL cholesterol and other cardiovascular disease (CVD) risk factors, and to identify determinants of the variability in LDL cholesterol response. METHODS: Healthy males (n = 109, mean ± SD age 48 ± 11 y; BMI 25.1 ± 3.3 kg/m2), consumed a higher-SFA/lower-UFA diet for 4 wk, followed by an isoenergetic, lower-SFA/higher-UFA diet for 4 wk (achieved intakes SFA:UFA as % total energy 19.1:14.8 and 8.9:24.5, respectively). Serum LDL cholesterol, CVD risk markers, peripheral blood mononuclear cell (PBMC) gene expression, and dietary intakes were assessed at baseline and the end of each diet. RESULTS: Transition from a higher-SFA/lower-UFA to a lower-SFA/higher-UFA diet significantly reduced fasting blood lipids: LDL cholesterol (-0.50 mmol/L; 95% confidence interval [CI]: -0.58, -0.42), high-density lipoprotein (HDL) cholesterol (-0.11 mmol/L; 95% CI: -0.14, -0.08), and total cholesterol (TC) (-0.65 mmol/L; 95% CI:-0.75, -0.55). The dietary exchange also reduced apolipoprotein (apo)B, TC:HDL cholesterol ratio, non-HDL cholesterol, E-selectin (P < 0.0001), and LDL subfraction composition (cholesterol [LDL-I and LDL-II], apoB100 [LDL-I and LDL-II], and TAG [LDL-II]) (P < 0.01). There was also an increase in plasma biomarkers of cholesterol intestinal absorption (ß-sitosterol, campesterol, cholestanol), and synthesis (desmosterol) (P < 0.0001) and fold change in PBMC LDL-receptor mRNA expression relative to the higher-SFA/lower-UFA diet (P = 0.035). Marked interindividual variation in the change in serum LDL cholesterol response (-1.39 to +0.77 mmol/L) to this dietary exchange was observed, with 33.7% of this variation explained by serum LDL cholesterol before the lower-SFA/higher-UFA diet and reduction in dietary SFA intake (adjusted R2 27% and 6.7%, respectively). APOE genotype was unrelated to serum LDL cholesterol response to SFA. CONCLUSIONS: These findings support the efficacy of United Kingdom SFA dietary guidelines for the overall lowering of serum LDL cholesterol but showed marked variation in LDL cholesterol response. Further identification of the determinants of this variation will facilitate targeting and increasing the efficacy of these guidelines. The RISSCI-1 study was registered with ClinicalTrials.Gov (No. NCT03270527).

Oxylipin secretion by human CD3+ T lymphocytes in vitro is modified by the exogenous essential fatty acid ratio and life stage.

Immune function changes across the life stages; for example, senior adults exhibit a tendency towards a weaker cell-mediated immune response and a stronger inflammatory response than younger adults. This might be partly mediated by changes in oxylipin synthesis across the life course. Oxylipins are oxidation products of polyunsaturated fatty acids (PUFAs) that modulate immune function and inflammation. A number of PUFAs are precursors to oxylipins, including the essential fatty acids (EFAs) linoleic acid (LA) and α-linolenic acid (ALA). LA and ALA are also substrates for synthesis of longer chain PUFAs. Studies with stable isotopes have shown that the relative amounts of LA and ALA can influence their partitioning by T lymphocytes between conversion to longer chain PUFAs and to oxylipins. It is not known whether the relative availability of EFA substrates influences the overall pattern of oxylipin secretion by human T cells or if this changes across the life stages. To address this, the oxylipin profile was determined in supernatants from resting and mitogen activated human CD3+ T cell cultures incubated in medium containing an EFA ratio of either 5:1 or 8:1 (LA : ALA). Furthermore, oxylipin profiles in supernatants of T cells from three life stages, namely fetal (derived from umbilical cord blood), adults and seniors, treated with the 5:1 EFA ratio were determined. The extracellular oxylipin profiles were affected more by the EFA ratio than mitogen stimulation such that n-3 PUFA-derived oxylipin concentrations were higher with the 5:1 EFA ratio than the 8:1 ratio, possibly due to PUFA precursor competition for lipoxygenases. 47 oxylipin species were measured in all cell culture supernatants. Extracellular oxylipin concentrations were generally higher for fetal T cells than for T cells from adult and senior donors, although the composition of oxylipins was similar across the life stages. The contribution of oxylipins towards an immunological phenotype might be due to the capacity of T cells to synthesize oxylipins rather than the nature of the oxylipins produced.

Exogenous tetracosahexaenoic acid modifies the fatty acid composition of human primary T lymphocytes and Jurkat T cell leukemia cells contingent on cell type.

Tetracosahexaenoic acid (24:6ω-3) is an intermediate in the conversion of 18:3ω-3 to 22:6ω-3 in mammals. There is limited information about whether cells can assimilate and metabolize exogenous 24:6ω-3. This study compared the effect of incubation with 24:6ω-3 on the fatty acid composition of two related cell types, primary CD3+ T lymphocytes and Jurkat T cell leukemia, which differ in the integrity of the polyunsaturated fatty acid (PUFA) biosynthesis pathway. 24:6ω-3 was only detected in either cell type when cells were incubated with 24:6ω-3. Incubation with 24:6ω-3 induced similar increments in the amount of 22:6ω-3 in both cell types and modified the homeoviscous adaptations fatty acid composition induced by activation of T lymphocytes. The effect of incubation with 18:3ω-3 compared to 24:6ω-3 on the increment in 22:6ω-3 was tested in Jurkat cells because primary T cells cannot convert 18:3ω-3 to 22:6ω-3. The increment in the 22:6ω-3 content of Jurkat cells incubated with 24:6ω-3 was 19.5-fold greater than that of cells incubated with 18:3ω-3. Acyl-coA oxidase siRNA knockdown decreased the amount of 22:6ω-3 and increased the amount of 24:6ω-3 in Jurkat cells. These findings show exogenous 24:6ω-3 can be incorporated into primary human T lymphocytes and Jurkat cells and induces changes in fatty acid composition consistent with its conversion to 22:6ω-3 via a mechanism involving peroxisomal ß-oxidation that is regulated independently from the integrity of the upstream PUFA synthesis pathway. One further implication is that consuming 24:6ω-3 may be an effective alternative means of achieving health benefits attributed to 20:5ω-3 and 22:6ω-3.

Effect of Dapagliflozin on Cardiac Function and Metabolic and Hormonal Responses to Exercise.

OBJECTIVE: This work aimed to investigate the effect of the SGLT2 inhibitor, dapagliflozin (DAPA), on cardiac function and the metabolic and hormonal response to moderate exercise in people with type 2 diabetes. METHODS: This was a double-blind, placebo-controlled crossover study with a 4-week washout period. Nine participants were randomly assigned to receive either 4 weeks of DAPA or 4 weeks of placebo. After each treatment, they underwent an exercise protocol with 2 consecutive 10-minute stages at a constant load corresponding to 40% and 70% maximal oxygen consumption (VO2max), coupled with hormonal and metabolic analysis. A blinded transthoracic echocardiogram was performed 3 days later. RESULTS: During the exercise protocol, glucose and lactate were lower (P < .0001 and P < .05, respectively) and ß-hydroxybutyrate (BOBH) and growth hormone (GH) were higher (P < .0005 and P = .01) following DAPA treatment compared to placebo. There was a trend for lower insulin with DAPA. Adrenalin, noradrenalin, and glucagon were not different. Following DAPA participants demonstrated an increased mean peak diastolic mitral annular velocity (e') in comparison to placebo (P = .03). The indexed left atrial volume and right ventricular e" were reduced following DAPA compared with placebo (P = .045 and P = .042, respectively). Arterial stiffness was not different between treatments (DAPA 9.35 ± 0.60 m/s; placebo 9.07 ± 0.72 m/s). CONCLUSION: During exercise, GH may be more important than catecholamines in driving the shift from glucose to fatty acid metabolism by SGLT2 inhibitors. The 4-week crossover design showed changes in cardiac function were rapid in onset and reversible.

Eicosapentaenoic acid-rich oil supplementation activates PPAR-γ and delays skin wound healing in type 1 diabetic mice.

Delayed wound healing is a devastating complication of diabetes and supplementation with fish oil, a source of anti-inflammatory omega-3 (ω-3) fatty acids including eicosapentaenoic acid (EPA), seems an appealing treatment strategy. However, some studies have shown that ω-3 fatty acids may have a deleterious effect on skin repair and the effects of oral administration of EPA on wound healing in diabetes are unclear. We used streptozotocin-induced diabetes as a mouse model to investigate the effects of oral administration of an EPA-rich oil on wound closure and quality of new tissue formed. Gas chromatography analysis of serum and skin showed that EPA-rich oil increased the incorporation of ω-3 and decreased ω-6 fatty acids, resulting in reduction of the ω-6/ω-3 ratio. On the tenth day after wounding, EPA increased production of IL-10 by neutrophils in the wound, reduced collagen deposition, and ultimately delayed wound closure and impaired quality of the healed tissue. This effect was PPAR-γ-dependent. EPA and IL-10 reduced collagen production by fibroblasts in vitro. In vivo, topical PPAR-γ-blockade reversed the deleterious effects of EPA on wound closure and on collagen organization in diabetic mice. We also observed a reduction in IL-10 production by neutrophils in diabetic mice treated topically with the PPAR-γ blocker. These results show that oral supplementation with EPA-rich oil impairs skin wound healing in diabetes, acting on inflammatory and non-inflammatory cells.

The [13 C]octanoic acid breath test for gastric emptying quantification: A focus on nutrition and modeling.

Gastric emptying (GE) is the process of food being processed by the stomach and delivered to the small intestine where nutrients such as lipids are absorbed into the blood circulation. The combination of an easy and inexpensive method to measure GE such as the CO2 breath test using the stable isotope [13 C]octanoic acid with semi-mechanistic modeling could foster a wider application in nutritional studies to further understand the metabolic response to food. Here, we discuss the use of the [13 C]octanoic acid breath test to label the solid phase of a meal, and the factors that influence GE to support mechanistic studies. Furthermore, we give an overview of existing mathematical models for the interpretation of the breath test data and how much nutritional studies could benefit from a physiological based pharmacokinetic model approach.

Dose Dependent Effects of Fructose and Glucose on de novo Palmitate and Glycerol Synthesis in an Enterocyte Cell Model.

SCOPE: Fructose exacerbates post-prandial hypertriacylglycerolaemia; perhaps partly due to increased enterocyte de novo lipogenesis (DNL). It is unknown whether this is concentration-dependent or if fructose has a greater effect on lipid synthesis than glucose. Dose-dependent effects of fructose and glucose on DNL and de novo triacylglycerol (TAG)-glycerol synthesis are investigated in a Caco-2 cell model. METHODS AND RESULTS: Caco-2 cells are treated for 96 h with 5, 25, or 50 mM fructose or glucose, or 12.5 mM fructose/12.5 mM glucose mix. DNL is measured following addition of [13 C2 ]-acetate to apical media. Separately, [13 C6 ]-fructose and [13 C6 ]-glucose are used to measure DNL and de novo TAG-glycerol synthesis. DNL from [13 C2 ]-acetate is detected following all treatments, with greater amounts in intracellular than secreted (media) samples (all p < 0.05). DNL from [13 C6 ]-fructose and [13 C6 ]-glucose is also measurable. Intracellular synthesis is concentration-dependent for both glucose (p = 0.003) and fructose (p = 0.034) tracers and is higher with 25 mM glucose than 25 mM fructose (p = 0.025). DNL from fructose and glucose is <1%, but up to 70% of de novo TAG-glycerol is synthesized from glucose or fructose. CONCLUSION: Fructose is not a major source of DNL in Caco-2 cells but contributes substantially to de novo TAG-glycerol synthesis.

Fatty acid composition and metabolic partitioning of α-linolenic acid are contingent on life stage in human CD3+ T lymphocytes.

Introduction: Immune function changes across the life course; the fetal immune system is characterised by tolerance while that of seniors is less able to respond effectively to antigens and is more pro-inflammatory than in younger adults. Lipids are involved centrally in immune function but there is limited information about how T cell lipid metabolism changes during the life course. Methods and Results: We investigated whether life stage alters fatty acid composition, lipid droplet content and α-linolenic acid (18:3ω-3) metabolism in human fetal CD3+ T lymphocytes and in CD3+ T lymphocytes from adults (median 41 years) and seniors (median 70 years). Quiescent fetal T cells had higher saturated (SFA), monounsaturated fatty acid (MUFA), and ω-6 polyunsaturated fatty acid (PUFA) contents than adults or seniors. Activation-induced changes in fatty acid composition differed between life stages. The principal metabolic fates of [13C]18:3ω-3 were constitutive hydroxyoctadecatrienoic acid synthesis and ß-oxidation and carbon recycling into SFA and MUFA. These processes declined progressively across the life course. Longer chain ω-3 PUFA synthesis was a relatively minor metabolic fate of 18:3ω-3 at all life stages. Fetal and adult T lymphocytes had similar lipid droplet contents, which were lower than in T cells from seniors. Variation in the lipid droplet content of adult T cells accounted for 62% of the variation in mitogen-induced CD69 expression, but there was no significant relationship in fetal cells or lymphocytes from seniors. Discussion: Together these findings show that fatty acid metabolism in human T lymphocytes changes across the life course in a manner that may facilitate the adaptation of immune function to different life stages.

The SGLT2 Inhibitor Dapagliflozin Increases the Oxidation of Ingested Fatty Acids to Ketones in Type 2 Diabetes.

OBJECTIVE: To investigate the mechanism for increased ketogenesis following treatment with the SGLT2 inhibitor dapagliflozin in people with type 2 diabetes. RESEARCH DESIGN AND METHODS: The design was a double-blind, placebo-controlled, crossover study with a 4-week washout period. Participants received dapagliflozin or placebo in random order for 4 weeks. After each treatment, they ingested 30 mL of olive oil containing [U-13C]palmitate to measure ketogenesis, with blood sampling for 480 min. Stable isotopes of glucose and glycerol were infused to measure glucose flux and lipolysis, respectively, at 450-480 min. RESULTS: Glucose excretion rate was higher and peripheral glucose uptake lower with dapagliflozin than placebo. Plasma ß-hydroxybutyrate (BOHB) concentrations and [13C2]BOHB concentrations were higher and glucose concentrations lower with dapagliflozin than placebo. Nonesterified fatty acids (NEFAs) were higher with dapagliflozin at 300 and 420 min, but lipolysis at 450-480 min was not different. Triacylglycerol at all time points and endogenous glucose production rate at 450-480 min were not different between treatments. CONCLUSIONS: The increase in ketone enrichment from the ingested palmitic acid tracer suggests that meal-derived fatty acids contribute to the increase in ketones during treatment with dapagliflozin. The increase in BOHB concentration with dapagliflozin occurred with only minimal changes in plasma NEFA concentration and no change in lipolysis. This finding suggests a metabolic switch to increase ketogenesis within the liver.

Splanchnic balance of free fatty acids, endocannabinoids, and lipids in subjects with nonalcoholic fatty liver disease.

BACKGROUND & AIMS: Animal studies suggest that endocannabinoids could contribute to the development of nonalcoholic fatty liver disease (NAFLD). In addition, NAFLD has been shown to be associated with multiple changes in lipid concentrations in liver biopsies. There are no data on splanchnic free fatty acid (FFA), glycerol, ketone body, endocannabinoid, and lipid fluxes in vivo in subjects with NAFLD. METHODS: We performed hepatic venous catheterization studies in combination with [(2)H(2)]palmitate infusion in the fasting state and during a low-dose insulin infusion in 9 subjects with various degrees of hepatic steatosis as determined using liver biopsy. Splanchnic balance of endocannabinoids and individual lipids was determined using ultra performance liquid chromatography coupled to mass spectrometry. RESULTS: Concentrations of the endocannabinoid 2-arachidonoylglycerol were higher in arterialized (91 ± 33 µg/L basally) than in hepatic venous (51 ± 19 µg/L; P < .05) plasma. Fasting arterial (r = 0.72; P = .031) and hepatic venous (r = 0.70; P = .037) concentrations of 2-arachidonoylglycerol were related positively to liver fat content. Analysis of fluxes of 85 different triglycerides showed that the fatty liver overproduces saturated triglycerides. In the plasma FFA fraction in the basal state, the relative amounts of palmitoleate and linoleate were lower and those of stearate and oleate were higher in the hepatic vein than in the artery. Absolute concentrations of all nontriglyceride lipids were comparable in arterialized venous plasma and the hepatic vein both in the basal and insulin-stimulated states. CONCLUSIONS: The human fatty liver takes up 2-arachidonoylglycerol and overproduces triacylglycerols containing saturated fatty acids, which might reflect increased de novo lipogenesis.