Reciprocal glycerolipid syntheses in skeletal muscle of obese rats.
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Animals↗
Biomedical subjects
Z K Guo
Publications and source records attributed to Z K Guo.
Accelerated intramyocellular triglyceride synthesis in skeletal muscle of high-fat-induced obese rats.
OBJECTIVE: To test the hypothesis that the synthesis of intramyocellular triglycerides (imcTG) in skeletal muscle is increased in obese rats in which the content of imcTG is known to be abnormally high. ANIMALS: Sprague-Dawley male lean and high-fat-induced obese rats were studied at the age of 4, 8 and 12 months after an overnight fast, awake. MEASUREMENTS: [U-(14)C]glycerol was continuously infused intravenously for 2 h followed by muscle biopsies, and intracellular glycerol incorporation into imcTG was determined. imcTG content, intramyocellular free glycerol concentration and specific activity, systemic glycerol flux and plasma glycerol, free fatty acid (FFA) and glucose concentrations were also determined. RESULTS: The rates of incorporation of intramyocellular glycerol into imcTG (nmol/g wet muscle/h) were markedly accelerated in obese rats compared to their lean littermates at all ages: 66+/-12 vs 12+/-2 (P=0.02) for gastrocnemius and 74+/-29 vs 31+/-7 (P=0.09) for soleus when 4 months old; 223+/-29 vs 58+/-27 (P=0.001) for gastrocnemius, 224+/-28 vs 70+/-21 (P=0.001) for soleus and 294+/-78 vs 49+/-22 (P=0.02) for tibialis anterior when 8 months old; and 25+/-4 vs 11+/-2 (P=0.01) for gastrocnemius and 22+/-8 vs 8.4+/-3 (P=0.04) for soleus when 12 months old. As expected, this was accompanied by a higher imcTG content in virtually all muscles at all ages tested. CONCLUSION: The synthesis of imcTG in skeletal muscle is grossly increased in obese rats, which likely contributes to abnormal imcTG accumulation.
Adipose Tissue↗
De novo lipogenesis in adipose tissue of lean and obese women: application of deuterated water and isotope ratio mass spectrometry.
OBJECTIVE: To evaluate the feasibility of using deuterated water and isotope ratio mass spectrometry to measure de novo fatty acid synthesis in adipose tissue, and to compare this parameter in obese and lean women. SUBJECTS: Six lean and six obese premenopausal Caucasian women in the main study and three obese Pima Indians in a pilot study. MEASUREMENTS: Deuterated water was administered orally twice daily for 14 days to create stable deuterium enrichment in body water, during which series of blood samples were collected to measure body water deuterium enrichment and deuterium incorporation into plasma total Triacylglycerol (TG) fatty acids and total cholesterol. Subcutaneous fat at different sites were sampled at the beginning and the end of deuterium administration to measure deuterium incorporation into TG fatty acids. RESULTS: Fractional de novo synthesis rate of TG fatty acids in adipose tissue was 0. 014+/-0.005 and 0.014+/-0.007% in lean and obese Caucasian women, corresponding to 2+/-0.7 and 5.6+/-3.2 g (P=0.3) of fatty acids synthesized daily, respectively. Plasma TG fatty acids and cholesterol synthesis rates were comparable to those reported previously. A pilot study showed that de novo lipid synthesis in adipose tissue of obese Pima Indians was also quantitatively minor. CONCLUSION: Human adipose tissue, like the liver, does not make a major contribution to whole body lipogenesis under eucaloric conditions. A combination of deuterated water and isotope ratio mass spectrometry is a useful research tool for studying accumulation of de novo synthesized lipids in human adipose tissue.
Adipocytes↗
Thrombopoietin: a potential T-helper lymphocyte stimulator. Change in T-lymphocyte composition and blood cytokine levels in thrombopoietin cDNA transferred mice.
The aim of this study was to evaluate the effect of thrombopoietin (TPO) on T lymphocyte in Balb/c mice delivered hTPO cDNA with plasmid vector. Both mature and immature T lymphocytes in central organs increased, but only the CD4+ subset was preferably proliferated in circulation. High serum IFN-gamma was coinciding with the declination of platelet counts, but TNF-alpha was positively associated with the platelet count, while high IL-2 level was similar to the course of TPO expression. Our data suggested that TPO is a stimulator for T lymphocytes, especially the CD4+ subset.
Animals↗
Compound-specific carbon isotope ratio determination of enriched cholesterol.
On-line gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS) was evaluated for use in stable isotope studies of human cholesterol metabolism. Calibration curves were constructed by analyzing underivatized and TMS-cholesterol over a range of 13C abundances from natural abundance to 0.05 mol of [3,4-13C]cholesterol per mole of unlabeled cholesterol (delta 13C -24 to 27/1000). The calibration curves were highly linear (r2 = 0.99) with slopes of 0.98 and 0.88 for underivatized and TMS-cholesterol, respectively. Higher precision of 13C/12C ratio determination was obtained using TMS-cholesterol, with a detection limit (2 SD) of 0.3/1000 or 0.004 mol% of [3,4-13C]cholesterol. By comparison standard GC/MS had a detection limit of 0.06 mol% for [3,4-13C]cholesterol. A 57-day study of cholesterol elimination was conducted in one human subject with oral administration of 50 mg of [3,4-13C]cholesterol. Peak enrichment was 9/1000 above baseline (40 times the detection limit) and could be followed for 40-50 days. The results indicate that GC/C/IRMS provides 15-fold lower detection limits for [3,4-13C]cholesterol than GC/MS and is useful for human studies of cholesterol metabolism.
Adult↗
Quantitation of positional isomers of deuterium-labeled glucose by gas chromatography/mass spectrometry.
A method for determining the site and extent of deuterium (D) labeling of glucose by GC/MS and mass fragmentography was developed. Under chemical and electron impact ionization, ion clusters m/z 328, 242, 217, 212, and 187 of glucose aldonitrile pentaacetate and m/z 331 and 169 of pentaacetate derivative were produced. From the mass spectra of 13C- and D-labeled reference compounds, glucose carbon and hydrogen (C-H) positions included in these fragments were deduced to be m/z 328 = C1-C6, 2,3,4,5,6,6-H6; m/z 331 = C1-C6, 1,2,3,4,5,6,6-H7; m/z 169 = C1-C6, 1,3,4,5,6,6-H6; m/z 187 = C3-C6, 3,4,5,6,6-H5; m/z 212 = C1-C5, 2,3,4,5-H4; m/z 217 = C4-C6, 4,5,6,6-H4; and m/z 242 = C1-C4, 2,3,4-H3. After correction for isotope discrimination and deuterium-hydrogen exchange, the D enrichment of these fragments can be quantitated using selective ion monitoring, and the D enrichment of all C-H positions can be obtained by the difference in enrichment of the corresponding ion pairs. The validity of this approach was tested by examining D enrichment of known mixtures of 1-d1-, 2-d1-, 3-d1-, and 5,6,6-d3-glucose with unlabeled glucose and D enrichment of perdeuterated glucose using these fragments. This method was used to determine deuterium incorporation in C1 through C6 of blood glucose in fasted (24 h) rats infused with deuterated water. The distribution of deuterium was similar to that found by Postle and Bloxham (1980, Biochem. J. 192, 65-73). Approximately one deuterium atom was incorporated into C5 and only 75% deuterium atom was incorporated into C2. The enrichment of C2 and C6 of glucose relative to that of water indicated that 74 +/- 9% of plasma glucose was newly formed 4 h after the onset of deuterium infusion, and gluconeogenesis accounted for about 76 +/- 7% of the glucose 6-phosphate flux.
Animals↗
Mass isotopomer pattern and precursor-product relationship.
The synthesis of a homonucleus polymer from its labeled precursor will lead to the formation of molecules with different masses. The distribution of these mass isotopomers is strictly a function of the enrichment of the 13C-labeled precursor, and can thus be used for the determination of the precursor enrichment and product dilution in the de novo synthesis of the polymer. We present here a study of the isotopomer pattern of a polymer of acetate in the form of glucose pentaacetate synthesized from 13C-enriched acetic anhydride. The molecular ion contains four acetyl units. Its synthesis is analogous to that of octanoic acid from acetyl coenzyme A. The process of obtaining the mass isotopomer distribution in the tetraacetyl moiety from the ion cluster of m/z 331 of glucose pentaacetate is illustrated. After correcting for the contribution of 13C natural abundance, the plot of the ratio of mass isotopomers (m4/m2) against the observed enrichment of the tetraacetate moiety yielded a straight line with a slope of 1.45. The ratio was not altered by dilution with pre-existing unenriched product, as predicted. The slope of the observed linear relationship agreed with the general formula (N-(j-1))/j for the ratio of any two consecutive mass isotopomers (mj/mj-1). Theoretical and practical aspects of determining precursor enrichment from isotopomer pattern in polymers are discussed.
Carbon Isotopes↗
Stimulation of glycogen synthesis by proglycosyn (LY177507) by isolated hepatocytes of normal and streptozotocin diabetic rats.
The phenacylimidazolium compound LY177507 was shown by Harris et al. (Harris, R. A., Yamanuchi, K., Roach, P. J., Yen, T. T., Dominiani, S. J., and Stephens, T. W. (1989) J. Biol. Chem. 264, 14674-14680) to stimulate glycogen synthesis greatly in isolated rat hepatocytes. We extended studies with this compound, designated proglycosyn (Yamaguchi, K., Stephens, T. W., Chikadar, K., Depaoli-Roach, A., And Harris, R. A. (1991) Diabetes 40, (Suppl. 1) 102 (abstr.] employing hepatocytes from normal and streptozotocin diabetic rats. Proglycosyn is more effective than amino acids in stimulating glycogen synthesis. In cells incubated with glucose, lactate, or dihydroxyacetone the effect of glutamine and proglycosyn was synergistic. In cells incubated with glucose plus lactate, or glucose plus dihydroxyacetone, the stimulation by the two agonists was additive. Proglycosyn diverted the gluconeogenic flux from glucose to glycogen. The maximal rates of glycogen deposition attained in the presence of glutamine and proglycosyn from cells incubated with glucose plus lactate, or glucose plus dihydroxyacetone, where about 80 and 110 mumols/h/g of liver, respectively. Proglycosyn depressed glycogenolysis in hepatocytes of fed rats and stimulated glycogen synthesis from lactate and dihydroxyacetone. The incorporation of [U-14C]glucose and [U-14C]lactate in these cells occurred in the presence of glycogen breakdown or exceeded net production, indicating the occurrence of recycling of glycogen in hepatocytes of fed rats. Hepatocytes from fasted streptozotocin diabetic rats contained high levels of glycogen. Glycogenolysis was markedly depressed by proglycosyn. Glycogen synthesis from lactate and dihydroxyacetone in these cells was stimulated by glutamine and proglycosyn in a fashion similar to that in cells from fasted control rats, and the rates of glycogen synthesis were similar in cells of control and diabetic rats. With glucose as sole substrate, glutamine did not stimulate glycogen synthesis. When both agonists were present, there was a marked synergism and substantial glycogen formation. Streptozotocin diabetic rats prior to the onset of cachexia have a normal capacity for glycogen synthesis.
Animals↗