21Standardising a dual x-ray absorptiometry (DXA) protocol is thought to provide a reliable 22 measurement of body composition. 23Purpose: We investigated the effects of manipulating muscle glycogen and creatine content 24 independently and additively on DXA estimates of lean mass. Results: Glycogen loading, both with and without creatine loading, resulted in substantial 34 increases in estimates of lean body mass (mean ± SD; 3.0 ± 0.7 % and 2.0 ± 0.9 %) and leg 35 lean mass (3.1 ± 1.8 %and 2.6 ± 1.0 %) respectively. A substantial decrease in leg lean mass 36 was observed following the glycogen depleting condition (-1.4 ± 1.6 %). Total body water 37 showed substantial increases following glycogen loading (2.3 ± 2.3 %), creatine loading (1.4 38 ± 1.9 %) and the combined treatment (2.3 ± 1.1 %).
The present work illustrated an accurate GC/MS measurement for the low isotopomer enrichment assay of formic acid, acetic acid, propionic aicd, butyric acid and pentanoic acid. The pentafluorobenzyl bromide derivatives of these very short chain fatty acids have high sensitivity of isotopoic enrichment due to their low natural isotopomer distribution in negative chemical ionization mass spectrometric mode. Pentafluorobenzyl bromide derivatization reaction was optimized in terms of pH, temperature, reaction time and the amount of pentafluorobenzyl bromide versus to sample. The precision, stability and accuracy of this method for the isotopomer analysis were validated. This method was applied to measure the enrichments of formic acid, acetic acid and propionic acid in the perfusate from rat liver exposed to Krebs-Ringer bicarbonate buffer only, 0-1 mM [3,4-13 C 2 ]-4-hydroxynonanoate and 0-2 mM of [5,6,[7][8][9][10][11][12][13] C 3 ]heptanoate. The enrichments of acetic acid and propionic acid in the perfusate are comparable to the labeling pattern of acetyl-CoA and propionyl-CoA in the rat liver tissues. The enrichment of acetic acid assay is much more sensitive and precise than the enrichment of acetyl-CoA by LC-MS/MS. The reversibility of propionyl-CoA from succinyl-CoA was confirmed by the low labeling of M1 and M2 of propionic acid from [5,6,[7][8][9][10][11][12][13] C 3 ]heptanoate perfusates.
Calcium levulinate (4-ketopentanoate) is used as an oral and parenteral source of calcium. We hypothesized that levulinate is converted in the liver to 4-hydroxypentanoate, a new drug of abuse, and that this conversion is accelerated by ethanol oxidation. We confirmed these hypotheses in live rats, perfused rat livers, and liver subcellular preparations. Levulinate is reduced to (R)-4-hydroxypentanoate by a cytosolic and a mitochondrial dehydrogenase, which are NADPH-and NADH-dependent, respectively. A mitochondrial dehydrogenase or racemase system also forms (S)-4-hydroxypentanoate. In livers perfused with [ 13 C 5 ]levulinate, there was substantial CoA trapping in levulinyl-CoA, 4-hydroxypentanoyl-CoA, and 4-phosphopentanoyl-CoA. This CoA trapping was increased by ethanol, with a 6-fold increase in the concentration of 4-phosphopentanoylCoA. Levulinate is catabolized by 3 parallel pathways to propionyl-CoA, acetyl-CoA, and lactate. Most intermediates of the 3 pathways were identified by mass isotopomer analysis and metabolomics. The production of 4-hydroxypentanoate from levulinate and its stimulation by ethanol is a potential public health concern.Levulinate (4-ketopentanoate) is a food additive allowed by the Food and Drug Administration. As a calcium salt, it has been used for many years as an oral and intravenous form of calcium administration (1, 2). It is listed in the pharmacopeias of a number of countries (USA, Europe, India, China, Japan, etc). It is also listed in quality control documents of the World Health Organization. The dry salt is sold on the internet as a non-prescription dietary supplement. To the best of our review of the literature, the catabolism of levulinate has not been investigated in mammalian cells. We found one report on the identification of the reduced form of levulinate, 4-hydroxypentanoate, in the urine of children with -ketothiolase deficiency treated with intravenous calcium levulinate (3). We also found an unexplained report of induction of lactic acidosis in premature babies treated with oral calcium levulinate for hypocalcemia (4).Our interest in levulinate arose from our recent study of the metabolism of 4-hydroxyacids, which are products of lipid peroxidation (C 9 , C 6 ) or drugs of abuse (C 4 , C 5 ) (5, 6). We showed that 4-hydroxyacids with 5 or more carbons are metabolized by two new pathways. The first pathway involves the isomerization of 4-hydroxyacyl-CoAs to 3-hydroxyacylCoAs via 4-phosphoacyl-CoAs, a new class of acyl-CoA esters. After isomerization, the 3-hydroxyacyl-CoAs are catabolized via classical -oxidation to acetyl-CoA and, in the case of odd-chain 4-hydroxyacids, to propionyl-CoA. The second pathway involves a sequence of -, ␣-, and -oxidation steps leading to acetyl-CoA, formate and, in the case of even chain 4-hydroxyacids, to propionyl-CoA.The five-carbon 4-hydroxypentanoate, as a racemic mixture, is a new drug of abuse used in lieu of 4-hydroxybutyrate, which is now a controlled substance in the United States (7-11). Based on our previous work...
Power output in the closing sprints of exhaustive TT cycling increased with CR ingestion despite a CR-mediated increase in weight. CR cosupplemented with carbohydrates may therefore be beneficial strategy for late-stage breakaway moments in endurance events.
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