Consequences of Lipid Remodeling of Adipocyte Membranes Being Functionally Distinct from Lipid Storage in Obesity.

Obesity is a complex disorder where the genome interacts with diet and environmental factors to ultimately influence body mass, composition, and shape. Numerous studies have investigated how bulk lipid metabolism of adipose tissue changes with obesity and, in particular, how the composition of triglycerides (TGs) changes with increased adipocyte expansion. However, reflecting the analytical challenge posed by examining non-TG lipids in extracts dominated by TGs, the glycerophospholipid composition of cell membranes has been seldom investigated. Phospholipids (PLs) contribute to a variety of cellular processes including maintaining organelle functionality, providing an optimized environment for membrane-associated proteins, and acting as pools for metabolites (e.g. choline for one-carbon metabolism and for methylation of DNA). We have conducted a comprehensive lipidomic study of white adipose tissue in mice which become obese either through genetic modification (ob/ob), diet (high fat diet), or a combination of the two, using both solid phase extraction and ion mobility to increase coverage of the lipidome. Composition changes in seven classes of lipids (free fatty acids, diglycerides, TGs, phosphatidylcholines, lyso-phosphatidylcholines, phosphatidylethanolamines, and phosphatidylserines) correlated with perturbations in one-carbon metabolism and transcriptional changes in adipose tissue. We demonstrate that changes in TGs that dominate the overall lipid composition of white adipose tissue are distinct from diet-induced alterations of PLs, the predominant components of the cell membranes. PLs correlate better with transcriptional and one-carbon metabolism changes within the cell, suggesting that the compositional changes that occur in cell membranes during adipocyte expansion have far-reaching functional consequences. Data are available at MetaboLights under the submission number: MTBLS1775.

Novel ketone diet enhances physical and cognitive performance.

Ketone bodies are the most energy-efficient fuel and yield more ATP per mole of substrate than pyruvate and increase the free energy released from ATP hydrolysis. Elevation of circulating ketones via high-fat, low-carbohydrate diets has been used for the treatment of drug-refractory epilepsy and for neurodegenerative diseases, such as Parkinson's disease. Ketones may also be beneficial for muscle and brain in times of stress, such as endurance exercise. The challenge has been to raise circulating ketone levels by using a palatable diet without altering lipid levels. We found that blood ketone levels can be increased and cholesterol and triglycerides decreased by feeding rats a novel ketone ester diet: chow that is supplemented with (R)-3-hydroxybutyl (R)-3-hydroxybutyrate as 30% of calories. For 5 d, rats on the ketone diet ran 32% further on a treadmill than did control rats that ate an isocaloric diet that was supplemented with either corn starch or palm oil (P < 0.05). Ketone-fed rats completed an 8-arm radial maze test 38% faster than did those on the other diets, making more correct decisions before making a mistake (P < 0.05). Isolated, perfused hearts from rats that were fed the ketone diet had greater free energy available from ATP hydrolysis during increased work than did hearts from rats on the other diets as shown by using [31P]-NMR spectroscopy. The novel ketone diet, therefore, improved physical performance and cognitive function in rats, and its energy-sparing properties suggest that it may help to treat a range of human conditions with metabolic abnormalities.-Murray, A. J., Knight, N. S., Cole, M. A., Cochlin, L. E., Carter, E., Tchabanenko, K., Pichulik, T., Gulston, M. K., Atherton, H. J., Schroeder, M. A., Deacon, R. M. J., Kashiwaya, Y., King, M. T., Pawlosky, R., Rawlins, J. N. P., Tyler, D. J., Griffin, J. L., Robertson, J., Veech, R. L., Clarke, K. Novel ketone diet enhances physical and cognitive performance.

Gene and metabolite expression dependence on body mass index in human myocardium.

We hypothesized that body mass index (BMI) dependent changes in myocardial gene expression and energy-related metabolites underlie the biphasic association between BMI and mortality (the obesity paradox) in cardiac surgery. We performed transcriptome profiling and measured a panel of 144 metabolites in 53 and 55, respectively, myocardial biopsies from a cohort of sixty-six adult patients undergoing coronary artery bypass grafting (registration: NCT02908009). The initial analysis identified 239 transcripts with biphasic BMI dependence. 120 displayed u-shape and 119 n-shape expression patterns. The identified local minima or maxima peaked at BMI 28-29. Based on these results and to best fit the WHO classification, we grouped the patients into three groups: BMI < 25, 25 ≤ BMI ≤ 32, and BMI > 32. The analysis indicated that protein translation-related pathways were downregulated in 25 ≤ BMI ≤ 32 compared with BMI < 25 patients. Muscle contraction transcripts were upregulated in 25 ≤ BMI ≤ 32 patients, and cholesterol synthesis and innate immunity transcripts were upregulated in the BMI > 32 group. Transcripts involved in translation, muscle contraction and lipid metabolism also formed distinct correlation networks with biphasic dependence on BMI. Metabolite analysis identified acylcarnitines and ribose-5-phosphate increasing in the BMI > 32 group and α-ketoglutarate increasing in the BMI < 25 group. Molecular differences in the myocardium mirror the biphasic relationship between BMI and mortality.

Metabolomics of the interaction between PPAR-alpha and age in the PPAR-alpha-null mouse.

Regulation between the fed and fasted states in mammals is partially controlled by peroxisome proliferator-activated receptor-alpha (PPAR-alpha). Expression of the receptor is high in the liver, heart and skeletal muscle, but decreases with age. A combined (1)H nuclear magnetic resonance (NMR) spectroscopy and gas chromatography-mass spectrometry metabolomic approach has been used to examine metabolism in the liver, heart, skeletal muscle and adipose tissue in PPAR-alpha-null mice and wild-type controls during ageing between 3 and 13 months. For the PPAR-alpha-null mouse, multivariate statistics highlighted hepatic steatosis, reductions in the concentrations of glucose and glycogen in both the liver and muscle tissue, and profound changes in lipid metabolism in each tissue, reflecting known expression targets of the PPAR-alpha receptor. Hepatic glycogen and glucose also decreased with age for both genotypes. These findings indicate the development of age-related hepatic steatosis in the PPAR-alpha-null mouse, with the normal metabolic changes associated with ageing exacerbating changes associated with genotype. Furthermore, the combined metabolomic and multivariate statistics approach provides a robust method for examining the interaction between age and genotype.

Clustered DNA damage induced by gamma radiation in human fibroblasts (HF19), hamster (V79-4) cells and plasmid DNA is revealed as Fpg and Nth sensitive sites.

The signature DNA lesion induced by ionizing radiation is clustered DNA damage. Gamma radiation-induced clustered DNA damage containing base lesions was investigated in plasmid DNA under cell mimetic conditions and in two cell lines, V79-4 (hamster) and HF19 (human), using bacterial endonucleases Nth (endonuclease III) and Fpg (formamidopyrimidine DNA glycosylase). Following irradiation with 60Co gamma-rays, induction of double-strand breaks (DSB) and clustered DNA damage, revealed as DSB by the proteins, was determined in plasmid using the plasmid-nicking assay and in cells by either conventional pulsed field gel electrophoresis or a hybridization assay, in which a 3 Mb restriction fragment of the X chromosome is used as a radioactive labeled probe. Enzyme concentrations (30-60 ng/microg DNA) were optimized to minimize visualization of background levels of endogenous DNA damage and DSB produced by non-specific cutting by Fpg and Nth in cellular DNA. 60Co gamma-radiation produces a 1.8-fold increase in the yields of both types of enzyme sensitive sites, visualized as DSB compared with that of prompt DSB in plasmid DNA. In mammalian cells, the increase in yields of clustered DNA damage containing either Fpg or Nth sensitive sites compared with that of prompt DSB is 1.4-2.0- and 1.8-fold, respectively. Therefore, clustered DNA damage is induced in cells by sparsely ionizing radiation and their yield is significantly greater than that of prompt DSB.

Processing of clustered DNA damage generates additional double-strand breaks in mammalian cells post-irradiation.

Clustered DNA damage sites, in which two or more lesions are formed within a few helical turns of the DNA after passage of a single radiation track, are signatures of DNA modifications induced by ionizing radiation in mammalian cells. Mutant hamster cells (xrs-5), deficient in non-homologous end joining (NHEJ), were irradiated at 37 degrees C to determine whether any additional double-strand breaks (DSBs) are formed during processing of gamma-radiation-induced DNA clustered damage sites. A class of non-DSB clustered DNA damage, corresponding to approximately 30% of the initial yield of DSBs, is converted into DSBs reflecting an artefact of preparation of genomic DNA for pulsed field gel electrophoresis. These clusters are removed within 4 min in both NHEJ-deficient and wild-type CHO cells. In xrs-5 cells, a proportion of non-DSB clustered DNA damage, representing approximately 10% of the total yield of non-DSB clustered DNA damage sites, are also converted into DSBs within approximately 30 min post-gamma but not post-alpha irradiation through cellular processing at 37 degrees C. That the majority of radiation-induced non-DSB clustered DNA damage sites are resistant to conversion into DSBs may be biologically significant at environmental levels of radiation exposure, as a non-DSB clustered damage site rather than a DSB, which only constitutes a minor proportion, is more likely to be induced in irradiated cells.

A combined metabolomic and proteomic investigation of the effects of a failure to express dystrophin in the mouse heart.

Muscle degeneration in the heart of 1-9 month-old mdx mice (a model for Duchenne muscular dystrophy) has been monitored using metabolomic and proteomic approaches. In both data sets, a pronounced aging trend was detected in control and mdx mice, and this trend was separate from the disease process. In addition, the characteristic increase in taurine associated with dystrophic tissue is correlated with proteins associated with oxidative phosphorylation and mitochondrial metabolism.

Applications of metabolomics to understanding obesity in mouse and man.

The functional genomic approach of metabolomics consists of the application of a global analytical tool to profile metabolism in a cell, tissue or organism. The most popular analytical tools include high-resolution (1)H nuclear magnetic resonance spectroscopy and mass spectrometry. Metabolomics is high throughput and relatively cheap on a per-sample basis and, hence, ideal for collecting large data sets. Biofluids are being used to follow the progression of obesity both in animal models and humans, while tissue extracts can be examined to probe the mechanisms responsible for these biofluid changes. Given these benefits and the results already produced in the field, metabolomics will play an increasing role in understanding the progression of obesity.