Adipocytes store excess energy in the form of triglycerides and signal the levels of stored energy to the brain. Here we show that adipocyte-specific deletion of Arntl (also known as Bmal1), a gene encoding a core molecular clock component, results in obesity in mice with a shift in the diurnal rhythm of food intake, a result that is not seen when the gene is disrupted in hepatocytes or pancreatic islets. Changes in the expression of hypothalamic neuropeptides that regulate appetite are consistent with feedback from the adipocyte to the central nervous system to time feeding behavior. Ablation of the adipocyte clock is associated with a reduced number of polyunsaturated fatty acids in adipocyte triglycerides. This difference between mutant and wild-type mice is reflected in the circulating concentrations of polyunsaturated fatty acids and nonesterified polyunsaturated fatty acids in hypothalamic neurons that regulate food intake. Thus, this study reveals a role for the adipocyte clock in the temporal organization of energy regulation, highlights timing as a modulator of the adipocyte-hypothalamic axis and shows the impact of timing of food intake on body weight.

Blood plasma has gained protagonism in lipidomics studies due to its availability, uncomplicated collection and preparation, and informative readout of physiological status. At the same time, it is also technically challenging to analyze due to its complex lipid composition affected by many factors, which can hamper the throughput and/or lipidomics coverage. To tackle these issues, we developed a comprehensive, high throughput, and quantitative mass spectrometry-based shotgun lipidomics platform for blood plasma lipid analyses. The main hallmarks of this technology are (i) it is comprehensive, covering 22 quantifiable different lipid classes encompassing more than 200 lipid species; (ii) it is amenable to high-throughput, with less than 5 min acquisition time allowing the complete analysis of 200 plasma samples per day; (iii) it achieves absolute quantification, by inclusion of internal standards for every lipid class measured; (iv) it is highly reproducible, achieving an average coefficient of variation of <10% (intra-day), approx. 10% (inter-day), and approx. 15% (inter-site) for most lipid species; (v) it is easily transferable allowing the direct comparison of data acquired in different sites. Moreover, we thoroughly assessed the influence of blood stabilization with different anticoagulants and freeze-thaw cycles to exclude artifacts generated by sample preparation.Practical applications: This shotgun lipidomics platform can be implemented in different laboratories without compromising reproducibility, allowing multi-site studies and inter-laboratory comparisons. This possibility combined with the high-throughput, broad lipidomic coverage and absolute quantification are important aspects for clinical applications and biomarker research.

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Sunburn is a commonly occurring acute inflammatory process, with dermal vasodilatation and leukocyte infiltration as central features. Ultraviolet (UV) B-induced hydrolysis of membrane phospholipids releases polyunsaturated fatty acids, and their subsequent metabolism by cyclooxygenases (COXs) and lipoxygenases (LOXs) may produce potent eicosanoid mediators modulating different stages of the inflammation. Our objective was to identify candidate eicosanoids formed during the sunburn reaction in relation to its clinical and histological course. We exposed skin of healthy humans (n=32) to UVB and, for 72 h, examined expression of proinflammatory and anti-inflammatory eicosanoids using LC/ESI-MS/MS, and examined immunohistochemical expression of COX-2, 12-LOX, 15-LOX, and leukocyte markers, while quantifying clinical erythema. We show that vasodilatory prostaglandins (PGs) PGE2, PGF2α, and PGE3 accompany the erythema in the first 24–48 h, associated with increased COX-2 expression at 24 h. Novel, potent leukocyte chemoattractants 11-, 12-, and 8-monohydroxy-eicosatetraenoic acid (HETE) are elevated from 4 to 72 h, in association with peak dermal neutrophil influx at 24 h, and increased dermal CD3+ lymphocytes and 12- and 15-LOX expression from 24 to 72 h. Anti-inflammatory metabolite 15-HETE shows later expression, peaking at 72 h. Sunburn is characterized by overlapping sequential profiles of increases in COX products followed by LOX products that may regulate subsequent events and ultimately its resolution.—Rhodes, L. E., Gledhill, K., Masoodi, M., Haylett, A. K., Brownrigg, M., Thody, A. J., Tobin, D. J., Nicolaou, A. The sunburn response in human skin is characterized by sequential eicosanoid profiles that may mediate its early and late phases.

Medium-chain triglycerides have been used as part of a ketogenic diet effective in reducing epileptic episodes. The health benefits of the derived medium-chain fatty acids (MCFAs) are thought to result from the stimulation of liver ketogenesis providing fuel for the brain. We tested whether MCFAs have direct effects on energy metabolism in induced pluripotent stem cell-derived human astrocytes and neurons. Using single-cell imaging, we observed an acute pronounced reduction of the mitochondrial electrical potential and a concomitant drop of the NAD(P)H signal in astrocytes, but not in neurons. Despite the observed effects on mitochondrial function, MCFAs did not lower intracellular ATP levels or activate the energy sensor AMP-activated protein kinase. ATP concentrations in astrocytes were unaltered, even when blocking the respiratory chain, suggesting compensation through accelerated glycolysis. The MCFA decanoic acid (300 μM) promoted glycolysis and augmented lactate formation by 49.6%. The shorter fatty acid octanoic acid (300 μM) did not affect glycolysis but increased the rates of astrocyte ketogenesis 2.17-fold compared with that of control cells. MCFAs may have brain health benefits through the modulation of astrocyte metabolism leading to activation of shuttle systems that provide fuel to neighboring neurons in the form of lactate and ketone bodies.-Thevenet, J., De Marchi, U., Santo Domingo, J., Christinat, N., Bultot, L., Lefebvre, G., Sakamoto, K., Descombes, P., Masoodi, M., Wiederkehr, A. Medium-chain fatty acids inhibit mitochondrial metabolism in astrocytes promoting astrocyte-neuron lactate and ketone body shuttle systems.

Prostanoids are potent mediators of many physiological and pathophysiological processes. Of the many analytical methodologies used for their qualitative and quantitative analysis, electrospray tandem mass spectrometry coupled to liquid chromatography (ESI-LC-MS/MS) offers a rapid, sensitive and versatile system applicable to lipidomic analyses. We have developed an ESI-LC-MS/MS assay for twenty-seven mediators including prostaglandins, prostacyclines, thromboxanes, dihydroprostaglandins and isoprostanes. The assay was liner over the concentration range 1-100 pg/μL. The limits of detection and quantitation were 0.5-50 pg and 2-100 pg respectively, whilst recoveries were from 83-116 % depending on the metabolite. The assay can be applied to profiling prostanoids produced by a variety of biological fluids and extracts including brain, liver, plasma and urine, facilitating thus our understanding of the role of these lipid mediators in health and disease, as well as assisting in drug development.