Uptake of 13C-tracer arachidonate and gamma-linolenate by the brain and liver of the suckling rat observed using 13C-NMR

Metabolism of uniformly labeled 13C-eicosapentaenoic acid and 13C-arachidonic acid in young and old men

Background: Plasma eicosapentaenoic acid (EPA) and arachidonic acid (AA) concentrations increase with age.Objective: The aim of this study was to evaluate EPA and AA metabolism in young and old men by using uniformly labeled carbon-13 (¹³C) fatty acids.Design: Six young (∼25 y old) and 6 old (∼75 y old) healthy men were recruited. Each participant consumed a single oral dose of 35 mg ¹³C-EPA and its metabolism was followed in the course of 14 d in the plasma and 28 d in the breath. After the washout period of ≥28 d, the same participants consumed a single oral dose of 50 mg ¹³C-AA and its metabolism was followed for 28 d in plasma and breath.Results: There was a time × age interaction for ¹³C-EPA (P_{time × age} = 0.008), and the shape of the postprandial curves was different between young and old men. The ¹³C-EPA plasma half-life was ∼2 d for both young and old men (P = 0.485). The percentage dose recovered of ¹³C-EPA per hour as ¹³CO₂ and the cumulative β-oxidation of ¹³C-EPA did not differ between young and old men. At 7 d, however, old men had a >2.2-fold higher plasma ¹³C-DHA concentration synthesized from ¹³C-EPA compared with young men (P_age = 0.03). ¹³C-AA metabolism was not different between young and old men. The ¹³C-AA plasma half-life was ∼4.4 d in both young and old participants (P = 0.589).Conclusions: The metabolism of ¹³C-AA was not modified by age, whereas ¹³C-EPA metabolism was slightly but significantly different in old compared with young men. The higher plasma ¹³C-DHA seen in old men may be a result of slower plasma DHA clearance with age. This trial was registered at clinicaltrials.gov as NCT02957188.

Cannabimimetic phytochemicals in the diet - an evolutionary link to food selection and metabolic stress adaptation?

The endocannabinoid system (ECS) is a major lipid signalling network that plays important pro-homeostatic (allostatic) roles not only in the nervous system but also in peripheral organs. There is increasing evidence that there is a dietary component in the modulation of the ECS. Cannabinoid receptors in hominids co-evolved with diet, and the ECS constitutes a feedback loop for food selection and energy metabolism. Here, it is postulated that the mismatch of ancient lipid genes of hunter-gatherers and pastoralists with the high-carbohydrate diet introduced by agriculture could be compensated for via dietary modulation of the ECS. In addition to the fatty acid precursors of endocannabinoids, the potential role of dietary cannabimimetic phytochemicals in agriculturist nutrition is discussed. Dietary secondary metabolites from vegetables and spices able to enhance the activity of cannabinoid-type 2 (CB₂ ) receptors may provide adaptive metabolic advantages and counteract inflammation. In contrast, chronic CB₁ receptor activation in hedonic obese individuals may enhance pathophysiological processes related to hyperlipidaemia, diabetes, hepatorenal inflammation and cardiometabolic risk. Food able to modulate the CB₁ /CB₂ receptor activation ratio may thus play a role in the nutrition transition of Western high-calorie diets. In this review, the interplay between diet and the ECS is highlighted from an evolutionary perspective. The emerging potential of cannabimimetic food as a nutraceutical strategy is critically discussed.

LINKED ARTICLES

This article is part of a themed section on Principles of Pharmacological Research of Nutraceuticals. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.11/issuetoc.

(13)C-NMR isotopomer distribution analysis: a method for measuring metabolic fluxes in condensation biosynthesis

(13)C NMR spectroscopy associated with the use of (13)C-enriched substrates is a powerful tool to investigate intracellular metabolism because of the wealth of information contained in the distribution of isotopes in key metabolites. A new method of using (13)C label distribution measurements in carbon skeletons of metabolites to estimate metabolic fluxes through biochemical reaction networks is presented here. This method can be applied to metabolite synthesis occurring by condensation reactions of the type nA --> B, where n is the number of precursor A molecules needed to synthesize one molecule of product B. NMR isotopomer distribution analysis (NMR-IDA) involves the introduction of a (13)C-enriched precursor, and measurements of the (13)C positional enrichments at just one carbon atom position of the product B via (13)C NMR spectroscopy. Information on isotopomer distribution is obtained, and data are analyzed according to a mathematical model based on multinomial probability expressions to obtain the best fit between theoretical and experimental (13)C label distribution. The use of the NMR-IDA method allows for estimation of two key parameters representing the fractional flux of (13)C-enriched tracer A molecules to total precursor A pool and the fraction of product B synthesized in the presence of a (13)C-enriched source, respectively. A practical example of NMR-IDA application to fatty acid synthesis from [(1,2 (13)C(2))acetyl]-L-carnitine in cultured primary astrocytes is also presented.

Stable isotope approaches, applications, and issues related to polyunsaturated fatty acid metabolism studies

The use of stable isotope tracers for investigating fatty acid metabolism in human subjects has increased substantially over the last decade. Advances in analytical instrumentation, commercial availability of labeled substrates, and safety considerations are major reasons for this increased use of stable isotope tracers. Several experimental design options are available for using either deuterium or carbon-13 as tracers for fatty acid and lipid studies. Options include feeding a pulse dose of labeled fat or a mixture containing two or more labeled fats. Multiple doses of the labeled fat can be fed at timed intervals to increase enrichments. Administration by injection or continuous intravenous infusion is an alternative. Another option is to use diets containing foods from plants that have slightly higher natural carbon-13 enrichment. Each basic experimental design has its specific strengths, and the best choice of experimental design depends on the study objectives. Stable isotope studies have been used to address a variety of questions related to unsaturated fatty acid metabolism in humans. Examples are provided that illustrate the use of stable isotopes to investigate oxidation of docosahexaenoic acid, desaturation of linoleic and linolenic acids in infants and adults, incorporation of long-chain n-6 and n-3 fatty acids, bioequivalency of linolenic acid in primates, 13C nuclear magnetic resonance spectra of arachidonic acid in living rat brain, and effect of triacylglycerol structure on absorption. Radioisotope and stable isotope tracer studies in animals and humans are responsible for much of our understanding of fatty acid and lipid metabolism. However, tracer studies have limitations, and there are some unresolved issues associated with isotope studies. Examples of unresolved issues are quantification of isotope data, validity of in vivo fatty acid metabolite results, kinetic modeling, subject variability, and use of blood lipid data as a reflection of tissue lipid metabolism. Resolving these issues, developing novel methodology, and applying stable isotope tracer methods to questions related to PUFA metabolism are broad areas of interesting and challenging research opportunities.

Determination of the phospholipid precursor of anandamide and other N-acylethanolamine phospholipids before and after sodium azide-induced toxicity in cultured neocortical neurons

Phospholipase D-mediated hydrolysis of N-acylethanolamine phospholipids (NAPEs) releases anandamide and other N-acylethanolamines, resulting in different actions at cellular targets in the CNS. Recently, we have demonstrated that these N-acyl lipids accumulate in cultured neocortical neurons subjected to sodium azide-induced cell injury. We here extend the information on the NAPE response, reporting on the composition of N-acylspecies of NAPE, employing a new methodological approach of HPLC-coupled electrospray ionization mass spectrometry. Exposure to sodium azide (5 mM) increased the total amount of NAPE threefold over control levels; however, no alteration of the relative composition of NAPE species was detected. The anandamide precursor (20 : 4-NAPE) constituted only 0.1% of all NAPEs detected in the neurons. Total NAPE species in control cells amounted to 956-1,060 pmol/10(7) cells. Moreover, we detected the presence of an unknown NAPE species with molecular weight identical to 20 : 4-NAPE. This may suggest the presence of a putative stereoisomer of the anandamide precursor with at least one trans-configured double bond in the N-arachidonoyl moiety. These results show that with the present method, neuronal NAPE species can be identified and quantified with respect to N-acyl composition, including a trans-isomer of the anandamide precursor. The anandamide precursor is up-regulated to the same extent as other NAPEs upon neuronal injury.